Sindroma Guillain Barre

SINDROMA GUILLAIN BARRE

Sindroma Guillain Barre (SGB) adalah suatu kelainan sistem saraf akut dan difus yang mengenai radiks spinalis dan saraf perifer, dan kadang-kadang juga saraf kranialis, yang biasanya timbul setelah suatu infeksi. Manifestasi klinis utama dari SGB adalah suatu kelumpuhan yang simetris tipe lower motor neuron dari otot-otot ekstremitas, badan dan kadang-kadang juga muka.

Sindroma Guillain Barre mempunyai banyak sinonim, antara lain : polineuritis akut pasca infeksi, polineuritis akut toksik, polineuritis febril, poliradikulopati dan acute ascending paralysis.Penyakit ini terdapat di seluruh dunia pada setiap musim, menyerang semua umur. SGB merupakan suatu penyakit autoimun, dimana proses imunologis tersebut langsung mengenai sistem saraf perifer. Mikroorganisme penyebab belum pernah ditemukan pada penderita penyakit ini dan pada pemeriksaan patologis tidak ditemukan tanda-tanda radang.Periode laten antara infeksi dan gejala polineuritis memberi dugaan bahwa kemungkinan kelainan yang terdapat disebabkan oleh suatu respons terhadap reaksi alergi saraf perifer. Pada banyak kasus, infeksi sebelumnya tidak ditemukan, kadang-kadang kecuali saraf perifer dan serabut spinal ventral dan dorsal, terdapat juga gangguan medula spinalis dan medula oblongata.Sampai saat ini belum ada terapi spesifik untuk SGB. Pengobatan secara simtomatis dan perawatan yang baik dapat memperbaiki prognosisnya.

INSIDENSBelum diketahui angka kejadian penyakit ini di Indonesia. Angka kejadian penyakit ini di seluruh dunia berkisar antara 1-1,5 kasus per 100.000 penduduk per tahun.Penyakit ini menyerang semua umur, tersering dikenai umur dewasa muda. Insidensi lebih tinggi pada perempuan daripada laki-laki dengan perbandingan 2 : 1, dan lebih banyak terjadi pada usia muda (umur 4-10 tahun). Umur termuda yang dilaporkan adalah 3 bulan dan tertua adalah 95 tahun, dan tidak ada hubungan antara frekuensi penyakit ini dengan suatu musim tertentu.ETIOLOGIDahulu sindrom ini diduga disebabkan oleh infeksi virus, tetapi akhir-akhir ini terungkap bahwa ternyata virus bukan sebagian penyebab. Teori yang dianut sekarang ialah suatu kelainan imunobiologik, baik secara primary immune response maupun immune mediated process.Pada umumnya sindrom ini sering didahului oleh influenza atau infeksi saluran nafas bagian atas atau saluran pencernaan. Penyebab infeksi pada umumnya virus dari kelompok herpes. Sindrom ini dapat pula didahului oleh vaksinasi, infeksi bakteri, gangguan endokrin, tindakan operasi, anestesi dan sebagainya.

PATOGENESIS Akibat suatu infeksi atau keadaan tertentu yang mendahului SGB akan timbul autoantibodi atau imunitas seluler terhadap jaringan sistim saraf-saraf perifer.Infeksi-infeksi meningokokus, infeksi virus, sifilis ataupun trauma pada medula spinalis,

dapat menimbulkan perlekatan-perlekatan selaput araknoid. Di negara-negara tropik penyebabnya adalah infeksi tuberkulosis. Pada tempat-tempat tertentu perlekatan pasca infeksi itu dapat menjirat radiks ventralis (sekaligus radiks dorsalis). Karena tidak segenap radiks ventralis terkena jiratan, namun kebanyakan pada yang berkelompokan saja, maka radiks-radiks yang diinstrumensia servikalis dan lumbosakralis saja yang paling umum dilanda proses perlekatan pasca infeksi. Oleh karena itu kelumpuhan LMN paling sering dijumpai pada otot-otot anggota gerak, kelompok otot-otot di sekitar persendian bahu dan pinggul. Kelumpuhan tersebut bergandengan dengan adanya defisit sensorik pada kedua tungkai atau otot-otot anggota gerak.Secara patologis ditemukan degenerasi mielin dengan edema yang dapat atau tanpa disertai infiltrasi sel. Infiltrasi terdiri atas sel mononuklear. Sel-sel infiltrat terutama terdiri dari sel limfosit berukuran kecil, sedang dan tampak pula, makrofag, serta sel polimorfonuklear pada permulaan penyakit. Setelah itu muncul sel plasma dan sel mast.Serabut saraf mengalami degenerasi segmental dan aksonal. Lesi ini bisa terbatas pada segmen proksimal dan radiks spinalis atau tersebar sepanjang saraf perifer. Predileksi pada radiks spinalis diduga karena kurang efektifnya permeabilitas antara darah dan saraf pada daerah tersebut.

GAMBARAN KLINISPenyakit infeksi dan keadaan prodromal :Pada 60-70 % penderita gejala klinis SGB didahului oleh infeksi ringan saluran nafas atau saluran pencernaan, 1-3 minggu sebelumnya (2). Sisanya oleh keadaan seperti berikut : setelah suatu pembedahan, infeksi virus lain atau eksantema pada kulit, infeksi bakteria, infeksi jamur, penyakit limfoma dan setelah vaksinasi influensa (1,4).

Masa latenWaktu antara terjadi infeksi atau keadaan prodromal yang mendahuluinya dan saat timbulnya gejala neurologis. Lamanya masa laten ini berkisar antara satu sampai 28 hari, rata-rata 9 hari (4). Pada masa laten ini belum ada gejala klinis yang timbul.

Keluhan utamaKeluhan utama penderita adalah prestasi pada ujung-ujung ekstremitas, kelumpuhan ekstremitas atau keduanya. Kelumpuhan bisa pada kedua ekstremitas bawah saja atau terjadi serentak pada keempat anggota gerak.

Gejala Klinis1.KelumpuhanManifestasi klinis utama adalah kelumpuhan otot-otot ekstremitas tipe lower motor neurone. Pada sebagian besar penderita kelumpuhan dimulai dari kedua ekstremitas bawah kemudian menyebar secara asenderen ke badan, anggota gerak atas dan saraf kranialis. Kadang-kadang juga bisa keempat anggota gerak dikenai secara serentak, kemudian menyebar ke badan dan saraf kranialis.Kelumpuhan otot-otot ini simetris dan diikuti oleh hiporefleksia atau arefleksia. Biasanya derajat kelumpuhan otot-otot bagian proksimal lebih berat dari bagian distal, tapi dapat juga sama beratnya, atau bagian distal lebih berat dari bagian proksimal (2,4).2.Gangguan sensibilitas

Parestesi biasanya lebih jelas pada bagian distal ekstremitas, muka juga bisa dikenai dengan distribusi sirkumoral (3). Defisit sensoris objektif biasanya minimal dan sering dengan distribusi seperti pola kaus kaki dan sarung tangan. Sensibilitas ekstroseptif lebih sering dikenal dari pada sensibilitas proprioseptif. Rasa nyeri otot sering ditemui seperti rasa nyeri setelah suatu aktifitas fisik (1,4).3.Saraf KranialisSaraf kranialis yang paling sering dikenal adalah N.VII. Kelumpuhan otot-otot muka sering dimulai pada satu sisi tapi kemudian segera menjadi bilateral, sehingga bisa ditemukan berat antara kedua sisi. Semua saraf kranialis bisa dikenai kecuali N.I dan N.VIII. Diplopia bisa terjadi akibat terkenanya N.IV atau N.III. Bila N.IX dan N.X terkena akan menyebabkan gangguan berupa sukar menelan, disfonia dan pada kasus yang berat menyebabkan kegagalan pernafasan karena paralisis n. laringeus (4).4.Gangguan fungsi otonomGangguan fungsi otonom dijumpai pada 25 % penderita SGB9 (4). Gangguan tersebut berupa sinus takikardi atau lebih jarang sinus bradikardi, muka jadi merah (facial flushing), hipertensi atau hipotensi yang berfluktuasi, hilangnya keringat atau episodic profuse diaphoresis. Retensi urin atau inkontinensia urin jarang dijumpai (1,4). Gangguan otonom ini jarang yang menetap lebih dari satu atau dua minggu.5.Kegagalan pernafasanKegagalan pernafasan merupakan komplikasi utama yang dapat berakibat fatal bila tidak ditangani dengan baik. Kegagalan pernafasan ini disebabkan oleh paralisis diafragma dan kelumpuhan otot-otot pernafasan, yang dijumpai pada 10-33 persen penderita (1,4).6.PapiledemaKadang-kadang dijumpai papiledema, penyebabnya belum diketahui dengan pasti. Diduga karena peninggian kadar protein dalam cairan otot yang menyebabkan penyumbatan villi arachoidales sehingga absorbsi cairan otak berkurang (4).7.Perjalanan penyakitPerjalan penyakit ini terdiri dari 3 fase, seperti pada gambar 1. Fase progresif dimulai dari onset penyakit, dimana selama fase ini kelumpuhan bertambah berat sampai mencapai maksimal. Fase ini berlangsung beberapa dari sampai 4 minggu, jarang yang melebihi 8 minggu (3,4).Segera setelah fase progresif diikuti oleh fase plateau, dimana kelumpuhan telah mencapai maksimal dan menetap. Fase ini bisa pendek selama 2 hari, paling sering selama 3 minggu, tapi jarang yang melebihi 7 minggu (3).Fase rekonvalesen ditandai oleh timbulnya perbaikan kelumpuhan ektremitas yang berlangsung selama beberapa bulan.Seluruh perjalanan penyakit SGB ini berlangsung dalam waktu yang kurang dari 6 bulan.Gambar 1. Perjalanan alamiah SGB skala waktu dan beratnya kelumpuhan bervariasi antara berbagai penderita SGB (3).

1.Variasi klinisDi samping penyakit SGB yang klasik seperti di atas, kita temui berbagai variasi klinis seperti yang dikemukakan oleh panitia ad hoc dari The National Institute of Neurological and Communicate Disorders and Stroke (NINCDS) pada tahun 1981 adalah sebagai berikut :Sindroma Miller-FisherDefisit sensoris kranialisPandisautonomia murniChronic acquired demyyelinative neuropathy.2.Pemeriksaan laboratoriumGambaran laboratorium yang menonjol adalah peninggian kadar protein dalam cairan otak : > 0,5 mg% tanpa diikuti oleh peninggian jumlah sel dalam cairan otak, hal ini disebut disosiasi sito-albuminik. Peninggian kadar protein dalam cairan otak ini dimulai pada minggu 1-2 dari onset penyakit dan mencapai puncaknya setelah 3-6 minggu (2,4,11). Jumlah sel mononuklear < 10 sel/mm3. Walaupun demikian pada sebagian kecil penderita tidak ditemukan peninggian kadar protein dalam cairan otak. Imunoglobulin serum bisa meningkat. Bisa timbul hiponatremia pada beberapa penderita yang disebabkan oleh SIADH (Sindroma Inapproriate Antidiuretik Hormone).3.Pemeriksaan elektrofisiologi (EMG)Gambaran elektrodiagnostik yang mendukung diagnosis SGB adalah (11) :Kecepatan hantaran saraf motorik dan sensorik melambatDistal motor retensi memanjangKecepatan hantaran gelombang-f melambat, menunjukkan perlambatan pada segmen proksimal dan radiks saraf.Di samping itu untuk mendukung diagnosis pemeriksaan elektrofisiologis juga berguna untuk menentukan prognosis penyakit : bila ditemukan potensial denervasi menunjukkan bahwa penyembuhan penyakit lebih lama dan tidak sembuh sempurna (12).

DIAGNOSISDiagnosis SGB berdasarkan gambaran klinis yang spesifik, disosiasi sito-albuminik dan kelainan elektrofisiologis. Kriteria diagnosis yang luas dipakai adalah kriteria diagnosis dari NINCDS tahun 1981 (11).

Tabel 1. Garis besar kriteria diagnosis SGBGambaran yang diperlukan untuk diagnosisKelemahan motorik yang progresisArefleksi atau hipofleksia

Gambaran yang mendukung diagnosisGambaran klinisProgresif cepatRelatif simetrisKeluhan gejala sensoris yang ringanDikenainya saraf otakPenyembuhan dimulai setelah 4 minggu fase progresif berakhirGangguan otonomAfebril pada saat onsetGambaran cairan otakPeninggian kadar protein setelah satu minggu onsetJumlah sel mononuklear cairan otak < 10 sel/mm3Gambaran EMGTerdapat perlambatan atau blok hantaran saraf

Gambaran yang meragukan diagnosisKelumpuhan asimetris yang menetapGangguan kandung kemih dan defikasi yang menetapGangguan kandung kemih dan defikasi pada onsetJumlah sel mononuklear dalam cairan otak > 50 sel mm3Terdapat leukosit PMN dalam cairan otakGangguan sensibilitas berbatas tegasGambaran yang menyingkirkan diagnosisTerdapat sangkaan adanya riwayat, gambaran klinis atau laboratorium dari :Pemakaian uap n-heksanPorfiria intermitten akutInfeksi difteriNeuropati karena keracunan timah hitamPoliomielitis, botulisme, histeri atau neuropati toksik

DIAGNOSIS BANDINGDiagnosis banding dari SGB adalah polimielitis, botulisme, hysterical paralysis, neuropati toksik (misalnya karena nitrofurantoin, dapsone, organofosfat), diphtheric paralysis, porfiria intermitten akut, neuropati karena timbal, mielitis akut (2,4,11).

PROGNOSISDahulu sebelum adanya ventilasi buatan lebih kurang 20 % penderita meninggal oleh karena kegagalan pernafasan. Sekarang ini kematian berkisar antara 2-10 % (1,3,6), dengan penyebab kematian oleh karena kegagalan pernafasan, gangguan fungsi otonom, infeksi paru dan emboli paru.Sebagian besar penderita (60-80 %) sembuh secara sempurna dalam waktu enam bulan. Sebagian kecil (7-22 %) sembuh dalam waktu 12 bulan dengan kelainan motorik ringan dan atrofi otot-otot kecil di tangan dan kaki (2,3). Kira-kira 3-5 % penderita mengalami relaps (2).

TERAPISampai saat ini belum ada pengobatan spesifik untuk SGB, pengobatan terutama secara simptomatis. Tujuan utama pengobatan adalah perawatan yang baik dan memperbaiki prognosisnya.1.Perawatan umum dan fisioterapi (1,4,13)Perawatan yang baik sangat penting dan terutama ditujukan pada perawatan kulit, kandung kemih. Saluran pencernaan, mulut, faring dan trakhea. Infeksi paru dan saluran kencing harus segera diobati.Respirasi diawasi secara ketat, terhadap perubahan kapasitas vital dan gas darah yang menunjukkan permulaan kegagalan pernafasan. Setiap ada tanda kegagalan pernafasan maka penderita harus segera dibantu dengan pernafasan buatan. Jika pernafasan buatan diperlukan untuk waktu yang lama maka trakheotomi harus dikerjakan.Fisioterapi yang teratur dan baik juga penting. Fisioterapi dada secara teratur untuk mencegah retensi sputum dan kolaps paru. Gerakan pasti pada kaki yang lumpuh mencegah deep voin thrombosis spint mungkin diperlukan untuk mempertahakan posisi anggota gerak yang lumpuh, dan kekakuan sendi dicegah dengan gerakan pasif.Segera setelah penyembuhan mulai (fase rekonvalesen) maka fisioterapi aktif dimulai untuk melatih dan meningkatkan kekuatan otot. Disfungsi otonom harus dicari dengan pengawasan teratur dari irama jantung dan tekanan darah. Bila ada nyeri otot dapat dapat diberikan analgetik.

2.Pertukaran plasmaPertukaran plasma (plasma exchange) bermanfaat bila dikerjakan dalam waktu 3 minggu pertama dari onset penyakit. Jumlah plasma yang dikeluarkan per exchange adalah 40-50 ml/kg. Dalam waktu 7-14 hari dilakukan tiga sampai lima kali exchange.

3.Kortikosteroid Walaupun telah melewati empat dekade pemakaian kortikosteroid pada SGB masih diragukan manfaatnya. Namun demikian ada yang berpendapat bahwa pemakaian kortikosteroid pada fase dini penyakit mungkin bermanfaat.

Guillain–Barré syndrome (GBS) (French pronunciation: [ ɡ iˈl ɛ ̃ baˈ ʁ e] , English

pronunciation: /ˈ ɡ iːlæn ˈb ɑ re ɪ / ), sometimes Landry's paralysis, is an acute inflammatory demyelinating polyneuropathy (AIDP), a disorder affecting the peripheral nervous system. Ascending paralysis, weakness beginning in the feet and hands and migrating towards the trunk, is the most typical symptom. It can cause life-threatening complications, particularly if the breathing muscles are affected or if there is dysfunction of the autonomic nervous system. The disease is usually triggered by an acute infection. Guillain–Barré syndrome is a form of peripheral neuropathy.

The diagnosis is usually made by nerve conduction studies. With prompt treatment by intravenous immunoglobulins or plasmapheresis, together with supportive care, the majority will recover completely. Guillain–Barré syndrome is rare, at 1–2 cases per 100,000 people annually, but is one of the leading causes of acute non-trauma-related

paralysis in the world. The syndrome is named after the French physicians Georges Guillain and Jean Alexandre Barré, who described it in 1916.

Contents[hide]

1 Classification 2 Signs and symptoms 3 Cause

o 3.1 Influenza o 3.2 Influenza vaccine

4 Diagnosis o 4.1 Diagnostic criteria

5 Management 6 Prognosis 7 Epidemiology 8 History 9 Notable cases 10 References

11 External links

[edit] Classification

Six different subtypes of Guillain–Barré syndrome exist:[citation needed]

Acute inflammatory demyelinating polyneuropathy (AIDP) is the most common form of GBS, and the term is often used synonymously with GBS. It is caused by an auto-immune response directed against Schwann cell membranes.

Miller Fisher syndrome (MFS) is a rare variant of GBS and manifests as a descending paralysis, proceeding in the reverse order of the more common form of GBS. It usually affects the eye muscles first and presents with the triad of ophthalmoplegia, ataxia, and areflexia. Anti-GQ1b antibodies are present in 90% of cases.

Acute motor axonal neuropathy (AMAN),[1] also known as Chinese paralytic syndrome, attacks motor nodes of Ranvier and is prevalent in China and Mexico. It is probably due to an auto-immune response directed against the axoplasm of peripheral nerves. The disease may be seasonal and recovery can be rapid. Anti-GD1a antibodies[2] are present. Anti-GD3 antibodies are found more frequently in AMAN.

Acute motor sensory axonal neuropathy (AMSAN) is similar to AMAN but also affects sensory nerves with severe axonal damage. Like AMAN, it is probably due to an auto-immune response directed against the axoplasm of peripheral nerves. Recovery is slow and often incomplete.[3]

Acute panautonomic neuropathy is the most rare variant of GBS, sometimes accompanied by encephalopathy. It is associated with a high mortality rate, owing

to cardiovascular involvement, and associated dysrhythmias. Impaired sweating, lack of tear formation, photophobia, dryness of nasal and oral mucosa, itching and peeling of skin, nausea, dysphagia, constipation unrelieved by laxatives or alternating with diarrhea occur frequently in this patient group. Initial nonspecific symptoms of lethargy, fatigue, headache, and decreased initiative are followed by autonomic symptoms including orthostatic lightheadedness, blurring of vision, abdominal pain, diarrhea, dryness of eyes, and disturbed micturition. The most common symptoms at onset are related to orthostatic intolerance, as well as gastrointestinal and sudomotor dysfunction (Suarez et al. 1994). Parasympathetic impairment (abdominal pain, vomiting, obstipation, ileus, urinary retention, dilated unreactive pupils, loss of accommodation) may also be observed.

Bickerstaff's brainstem encephalitis (BBE), is a further variant of Guillain–Barré syndrome. It is characterized by acute onset of ophthalmoplegia, ataxia, disturbance of consciousness, hyperreflexia or Babinski's sign. The course of the disease can be monophasic or remitting-relapsing. Large, irregular hyperintense lesions located mainly in the brainstem, especially in the pons, midbrain and medulla are described in the literature. BBE despite severe initial presentation usually has a good prognosis. Magnetic resonance imaging (MRI) plays a critical role in the diagnosis of BBE. A considerable number of BBE patients have associated axonal Guillain–Barré syndrome, indicative that the two disorders are closely related and form a continuous spectrum.

[edit] Signs and symptoms

The disorder is characterized by symmetrical weakness which usually affects the lower limbs first, and rapidly progresses in an ascending fashion. Patients generally notice weakness in their legs, manifesting as "rubbery legs" or legs that tend to buckle, with or without dysesthesias (numbness or tingling). As the weakness progresses upward, usually over periods of hours to days, the arms and facial muscles also become affected. Frequently, the lower cranial nerves may be affected, leading to bulbar weakness, oropharyngeal dysphagia (drooling, or difficulty swallowing and/or maintaining an open airway) and respiratory difficulties. Most patients require hospitalization and about 30% require ventilatory assistance.[4] Facial weakness is also commonly a feature, but eye movement abnormalities are not commonly seen in ascending GBS, but are a prominent feature in the Miller-Fisher variant (see below.) Sensory loss, if present, usually takes the form of loss of proprioception (position sense) and areflexia (complete loss of deep tendon reflexes), an important feature of GBS. Loss of pain and temperature sensation is usually mild. In fact, pain is a common symptom in GBS, presenting as deep aching pain, usually in the weakened muscles, which patients compare to the pain from overexercising. These pains are self-limited and should be treated with standard analgesics. Bladder dysfunction may occur in severe cases but should be transient. If severe, spinal cord disorder should be suspected.

Fever should not be present, and if it is, another cause should be suspected.

In severe cases of GBS, loss of autonomic function is common, manifesting as wide fluctuations in blood pressure, orthostatic hypotension, and cardiac arrhythmias.

Acute paralysis in Guillain–Barré syndrome may be related to sodium channel blocking factor in the cerebrospinal fluid (CSF). Significant issues involving intravenous salt and water administration may occur unpredictably in this patient group, resulting in SIADH. SIADH is one of the causes of hyponatremia and can be accompanied with various conditions such as malignancies, infections and nervous system diseases. Symptoms of Guillain-Barré syndrome such as general weakness, decreased consciousness, and seizure are similar to those of hyponatremia

The symptoms of Guillain–Barré syndrome are also similar to those for progressive inflammatory neuropathy.[5]

[edit] CauseStructure of a typical neuron

Neuron

DendriteSomaAxon

NucleusNode ofRanvier

Axon terminalSchwann cellMyelin sheath

All forms of Guillain–Barré syndrome are due to an immune response to foreign antigens (such as infectious agents) that is mistargeted at host nerve tissues instead. The targets of such immune attack are thought to be gangliosides, compounds naturally present in large quantities in human nerve tissues. The most common antecedent infection is the bacterium Campylobacter jejuni.[6][7] However, 60% of cases do not have a known cause. One study suggests that a minority of cases may be triggered by the influenza virus, or by an immune reaction to the influenza virus.[8]

The end result of such autoimmune attack on the peripheral nerves is damage to the myelin, the fatty insulating layer of the nerve, and a nerve conduction block, leading to a muscle paralysis that may be accompanied by sensory or autonomic disturbances.

However, in mild cases, nerve axon (the long slender conducting portion of a nerve) function remains intact and recovery can be rapid if remyelination occurs. In severe cases, axonal damage occurs, and recovery depends on the regeneration of this important tissue. Recent studies on the disorder have demonstrated that approximately 80% of the patients have myelin loss, whereas, in the remaining 20%, the pathologic hallmark of the disorder is indeed axon loss.

Guillain-Barré, unlike disorders such as multiple sclerosis (MS) and Lou Gehrig's disease (ALS), is a peripheral nerve disorder and does not generally cause nerve damage to the brain or spinal cord.

[edit] Influenza

While influenza vaccines have sometimes been suspected to raise the incidence of GBS, the evidence is equivocal. On the other hand, getting infected by influenza itself increases both the risk of death (up to 1 in 10,000) and increases the risk of developing GBS to a much higher level than the highest level of suspected vaccine involvement (approx. 10 times higher by recent estimates).[9][10]

[edit] Influenza vaccine

GBS may be a rare side-effect of influenza vaccines; a study of the Vaccine Adverse Event Reporting System (VAERS) indicates that it is reported as an adverse event potentially associated with the vaccine at a rate of 1 per million vaccines (over the normal risk).[11] There were reports of GBS affecting 10 per million who had received swine flu immunizations in the 1976 U.S. outbreak of swine flu—25 of which resulted in death from severe pulmonary complications, leading the government to end that immunization campaign. (By comparison, the average flu season kills around 30,000 people in the United States).[12] However, the role of the vaccine even in those 25 cases in 1976 has remained unclear, partly because GBS had an unknown but very low incidence rate in the general population making it difficult to assess whether the vaccine was really increasing the risk for GBS. Later research has pointed to the absence of, or only a very small increase in, the GBS risk due to the 1976 swine flu vaccine.[13] Furthermore, the GBS may not have been directly due to the vaccine but to a bacterial contamination of the 1976 vaccine.[14]

Since 1976, no other influenza vaccines have been linked to GBS, though as a precautionary principle, caution is advised for certain individuals, particularly those with a history of GBS.[15][16]

From October 6 to November 24, 2009, the U.S. CDC, through the VAERS reporting system, received ten reports of Guillain-Barré syndrome cases associated with the H1N1

vaccine and identified two additional probable cases from VAERS reports (46.2 million doses were distributed within the U.S. during this time). Only four cases, however, meet the Brighton Collaboration Criteria for Guillain–Barré syndrome, while four do not meet the criteria and four remain under review.[17] A preliminary report by the CDC's Emerging Infections Programs (EIP) calculates the rate of GBS observed in patients who previously received the 2009 H1N1 influenza vaccination is an excess of 0.8 per million cases, which is on par with the rate seen with the seasonal trivalent influenza vaccine.[18]

Although one review gives an incidence of about one case per million vaccinations,[19] a large study in China, reported in the NEJM covering close to 100 million doses of vaccine against the 2009 H1N1 "swine" flu found only eleven cases of Guillain-Barré syndrome (0.1%) total incidence in persons vaccinated, actually lower than the normal rate of the disease in China, and no other notable side effects; "The risk-benefit ratio, which is what vaccines and everything in medicine is about, is overwhelmingly in favor of vaccination."[20]

[edit] Diagnosis

The diagnosis of GBS usually depends on findings such as rapid development of muscle paralysis, areflexia, absence of fever, and a likely inciting event. Cerebrospinal fluid analysis (through a lumbar spinal puncture) and electrodiagnostic tests of nerves and muscles (such as nerve conduction studies) are common tests ordered in the diagnosis of GBS.

cerebrospinal fluid

Typical CSF findings include albumino-cytological dissociation. As opposed to infectious causes, this is an elevated protein level (100–1000 mg/dL), without an accompanying increased cell count pleocytosis. A sustained increased white blood cell count may indicate an alternative diagnosis such as infection.

Electrodiagnostics

Electromyography (EMG) and nerve conduction study (NCS) may show prolonged distal latencies, conduction slowing, conduction block, and temporal dispersion of compound action potential in demyelinating cases. In primary axonal damage, the findings include reduced amplitude of the action potentials without conduction slowing.

[edit] Diagnostic criteria

Required:[citation needed]

Progressive, relatively symmetrical weakness of two or more limbs due to neuropathy

Areflexia Disorder course < 4 weeks

Exclusion of other causes (see below)

Supportive:[citation needed]

relatively symmetric weakness accompanied by numbness and/or tingling mild sensory involvement facial nerve or other cranial nerve involvement absence of fever typical CSF findings obtained from lumbar puncture electrophysiologic evidence of demyelination from electromyogram

Differential diagnosis:[citation needed]

acute myelopathies with chronic back pain and sphincter dysfunction botulism with early loss of pupillary reactivity and descending paralysis diphtheria with early oropharyngeal dysfunction Lyme disease polyradiculitis and other tick-borne paralyses porphyria with abdominal pain, seizures, psychosis vasculitis neuropathy poliomyelitis with fever and meningeal signs CMV polyradiculitis in immunocompromised patients critical illness neuropathy myasthenia gravis poisonings with organophosphate, poison hemlock, thallium, or arsenic intoxication with Karwinskia humboldtiana leaves or seeds paresis caused by West Nile virus spinal astrocytoma motor neurone disease West Nile virus can cause severe, potentially fatal neurological illnesses, which

include encephalitis, meningitis, Guillain-Barré syndrome, and anterior myelitis.

[edit] Management

Supportive care with monitoring of all vital functions is the cornerstone of successful management in the acute patient. Of greatest concern is respiratory failure due to paralysis of the diaphragm. Early intubation should be considered in any patient with a vital capacity (VC) <20 ml/kg, a negative inspiratory force (NIF) that is less negative (i.e., closer to zero) than -25 cmH2O, more than 30% decrease in either VC or NIF within 24 hours, rapid progression of disorder, or autonomic instability.

Once the patient is stabilized, treatment of the underlying condition should be initiated as soon as possible. Either high-dose intravenous immunoglobulins (IVIg) at 400 mg/kg for 5 days or plasmapheresis can be administered,[21][22] as they are equally effective and a combination of the two is not significantly better than either alone. Therapy is no longer effective two weeks after the first motor symptoms appear, so treatment should be instituted as soon as possible. IVIg is usually used first because of its ease of

administration and safety profile, with a total of five daily infusions for a total dose of 2 g/kg body weight (400 mg/kg each day). The use of intravenous immunoglobulins is not without risk, occasionally causing hepatitis, or in rare cases, renal failure if used for longer than five days. Glucocorticoids have not been found to be effective in GBS. If plasmapheresis is chosen, a dose of 40-50 mL/kg plasma exchange (PE) can be administered four times over a week.

Following the acute phase, the patient may also need rehabilitation to regain lost functions. This treatment will focus on improving ADL (activities of daily living) functions such as brushing teeth, washing, and getting dressed. Depending on the local structuring on health care, a team of different therapists and nurses will be established according to patient needs. An occupational therapist can offer equipment (such as wheelchair and special cutlery) to help the patient achieve ADL independence. A physiotherapist would plan a progressive training program and guide the patient to correct, functional movement, avoiding harmful compensations which might have a negative effect in the long run. A speech and language therapist would be essential in the patient regaining speaking and swallowing ability if they were intubated and received a tracheostomy. The speech and language therapist would also offer advice to the medical team regarding the swallowing abilities of the patient and would help the patient regain their communication ability pre-dysarthria. There would also be a doctor, nurse and other team members involved, depending on the needs of the patient. This team contribute their knowledge to guide the patient towards his or her goals, and it is important that all goals set by the separate team members are relevant for the patient's own priorities. After rehabilitation the patient should be able to function in his or her own home and attend necessary training as needed.

[edit] Prognosis

Most of the time recovery starts after the fourth week from the onset of the disorder. Approximately 80% of patients have a complete recovery within a few months to a year, although minor findings may persist, such as areflexia. About 5–10% recover with severe disability, with most of such cases involving severe proximal motor and sensory axonal damage with inability of axonal regeneration. However, this is a grave disorder and despite all improvements in treatment and supportive care, the death rate among patients with this disorder is still about 2–3% even in the best intensive care units. Worldwide, the death rate runs slightly higher (4%), mostly from a lack of availability of life support equipment during the lengthy plateau lasting four to six weeks, and in some cases up to one year, when a ventilator is needed in the worst cases. About 5–10% of patients have one or more late relapses, in which case they are then classified as having chronic inflammatory demyelinating polyneuropathy (CIDP).

Poor prognostic factors include: 1) age, over 40 years, 2) history of preceding diarrheal illness, 3) requiring ventilator support, 4) high anti-GM1 titre and 5) poor upper limb muscle strength.

[edit] Epidemiology

The incidence of GBS during pregnancy is 1.7 cases per 100,000 of the population.[23] The mother will generally improve with treatment but death of the fetus is a risk. The risk of Guillain–Barré syndrome increases after delivery, particularly during the first two weeks postpartum. There is evidence of Campylobacter jejuni as an antecedent infection in approximately 26% of disease cases, requiring special care in the preparation and handling of food. Congenital and neonatal Guillain–Barré syndrome have also been reported.[24]

[edit] History

The disorder was first described by the French physician Jean Landry in 1859. In 1916, Georges Guillain, Jean Alexandre Barré, and André Strohl diagnosed two soldiers with the illness and discovered the key diagnostic abnormality of increased spinal fluid protein production, but normal cell count.[25]

GBS is also known as acute idiopathic polyradiculoneuritis, acute idiopathic polyneuritis, French polio, Landry's ascending paralysis and Landry Guillain Barré syndrome.

Canadian neurologist C. Miller Fisher described the variant that bears his name in 1956.[26]

Myasthenia gravis (from Greek μύς "muscle", ἀσθένεια "weakness", and Latin: gravis "serious"; abbreviated MG) is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability. It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction,[1] inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated medically with cholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. The disease incidence is 3–30 cases per million and rising as a result of increased awareness.[2] MG must be distinguished from congenital myasthenic syndromes that can present similar symptoms but offer no response to immunosuppressive treatments.

Contents[hide]

1 Classification 2 Signs and symptoms 3 Pathophysiology

o 3.1 Associated condition o 3.2 In pregnancy

4 Diagnosis o 4.1 Physical examination o 4.2 Blood tests o 4.3 Neurophysiology o 4.4 Edrophonium test o 4.5 Imaging o 4.6 Pulmonary function test o 4.7 Pathological findings

5 Treatment o 5.1 Medication o 5.2 Plasmapheresis and IVIG o 5.3 Surgery

6 Prognosis 7 Epidemiology 8 Notable patients

o 8.1 Real o 8.2 Fictional

9 References

10 External links

[edit] Classification

The most widely accepted classification of myasthenia gravis is the Myasthenia Gravis Foundation of America Clinical Classification:[3]

Class I: Any eye muscle weakness, possible ptosis, no other evidence of muscle weakness elsewhere

Class II: Eye muscle weakness of any severity, mild weakness of other muscles o Class IIa: Predominantly limb or axial muscleso Class IIb: Predominantly bulbar and/or respiratory muscles

Class III: Eye muscle weakness of any severity, moderate weakness of other muscles

o Class IIIa: Predominantly limb or axial muscleso Class IIIb: Predominantly bulbar and/or respiratory muscles

Class IV: Eye muscle weakness of any severity, severe weakness of other muscles o Class IVa: Predominantly limb or axial muscles

o Class IVb: Predominantly bulbar and/or respiratory muscles (Can also include feeding tube without intubation)

Class V: Intubation needed to maintain airway

[edit] Signs and symptoms

Blepharoptosis of the left eye.

The hallmark of myasthenia gravis is fatigability. Muscles become progressively weaker during periods of activity and improve after periods of rest. Muscles that control eye and eyelid movement, facial expressions, chewing, talking, and swallowing are especially susceptible. The muscles that control breathing and neck and limb movements can also be affected. Often the physical examination yields results within normal limits.[4]

The onset of the disorder can be sudden. Often symptoms are intermittent. The diagnosis of myasthenia gravis may be delayed if the symptoms are subtle or variable.

In most cases, the first noticeable symptom is weakness of the eye muscles. In others, difficulty in swallowing and slurred speech may be the first signs. The degree of muscle weakness involved in MG varies greatly among patients, ranging from a localized form that is limited to eye muscles (ocular myasthenia), to a severe and generalized form in which many muscles - sometimes including those that control breathing - are affected. Symptoms, which vary in type and severity, may include asymmetrical ptosis (a drooping of one or both eyelids), diplopia (double vision) due to weakness of the muscles that control eye movements, an unstable or waddling gait, weakness in arms, hands, fingers, legs, and neck, a change in facial expression, dysphagia (difficulty in swallowing), shortness of breath and dysarthria (impaired speech, often nasal due to weakness of the velar muscles).

In myasthenic crisis a paralysis of the respiratory muscles occurs, necessitating assisted ventilation to sustain life. In patients whose respiratory muscles are already weak, crises may be triggered by infection, fever, an adverse reaction to medication, or emotional stress.[5] Since the heart muscle is only regulated by the autonomic nervous system, it is generally unaffected by MG.

[edit] Pathophysiology

A juvenile thymus. It shrinks with age.

Myasthenia gravis is an autoimmune channelopathy: it features antibodies directed against the body's own proteins. While various similar diseases have been linked to immunologic cross-reaction with an infective agent, there is no known causative pathogen that could account for myasthenia. There is a slight genetic predisposition: particular HLA types seem to predispose for MG (B8 and DR3 with DR1 more specific for ocular myasthenia). Up to 75% of patients have an abnormality of the thymus; 25% have a thymoma, a tumor (either benign or malignant) of the thymus, and other abnormalities are frequently found. The disease process generally remains stationary after thymectomy (removal of the thymus).

The acetylcholine receptor.

In MG, the auto-antibodies most commonly against the nicotinic acetylcholine receptor (nAChR),[6] the receptor in the motor end plate for the neurotransmitter acetylcholine that stimulates muscular contractions. Some forms of the antibody impair the ability of acetylcholine to bind to receptors. Others lead to the destruction of receptors, either by complement fixation or by inducing the muscle cell to eliminate the receptors through endocytosis.

The antibodies are produced by plasma cells, derived from B-cells. B-cells convert into plasma cells by T-helper cell stimulation. In order to carry out this activation, T-helpers must first be activated themselves, which is done by binding of the T-cell receptor (TCR) to the acetylcholine receptor antigenic peptide fragment (epitope) resting within the

major histocompatibility complex of an antigen presenting cells. Since the thymus plays an important role in the development of T-cells and the selection of TCR myasthenia gravis is closely associated with thymoma . The exact mechanisms are however not convincingly clarified although resection of the thymus (thymectomy) in MG patients without a thymus neoplasm often have positive results.

In normal muscle contraction, cumulative activation of the nAChR leads to influx of sodium ions which in turn causes the depolarization of muscle cell and subsequent opening of voltage gated sodium channels. This ion influx then travels down the cell membranes via T-tubules and, via calcium channel complexes leads to the release of calcium from the sarcoplasmic reticulum. Only when the levels of calcium inside the muscle cell are high enough will it contract. Decreased numbers of functioning nAChRs therefore impairs muscular contraction by limiting depolarization. In fact, MG causes the motor neuron action potential to muscular twitch ratio to vary from the non-pathological one to one ratio.

It has recently been realized that a second category of gravis is due to auto-antibodies against the MuSK protein (muscle specific kinase), a tyrosine kinase receptor which is required for the formation of the neuromuscular junction. Antibodies against MuSK inhibit the signaling of MuSK normally induced by its nerve-derived ligand, agrin. The result is a decrease in patency of the neuromuscular junction, and the consequent symptoms of MG.

People treated with penicillamine can develop MG symptoms. Their antibody titer is usually similar to that of MG, but both the symptoms and the titer disappear when drug administration is discontinued.

MG is more common in families with other autoimmune diseases. A familial predisposition is found in 5% of the cases. This is associated with certain genetic variations such as an increased frequency of HLA-B8 and DR3. People with MG suffer from co-existing autoimmune diseases at a higher frequency than members of the general population. Of particular mention is co-existing thyroid disease where episodes of hypothyroidism may precipitate a severe exacerbation.

The acetylcholine receptor is clustered and anchored by the Rapsyn protein, research in which might eventually lead to new treatment options.[7]

[edit] Associated condition

Myasthenia Gravis is associated with various autoimmune diseases,[8] including:

Thyroid diseases, including Hashimoto's thyroiditis and Graves' disease Diabetes mellitus type 1 Rheumatoid arthritis Lupus , and Demyelinating CNS diseases

Seropositive and "double-seronegative" patients often have thymoma or thymic hyperplasia. However, anti-MuSK positive patients do not have evidence of thymus pathology.

[edit] In pregnancy

In the long term, pregnancy does not affect myasthenia gravis. Up to 10% of infants with parents affected by the condition are born with transient (periodic) neonatal myasthenia (TNM) which generally produces feeding and respiratory difficulties.[9] TNM usually presents as poor sucking and generalized hypotonia (low muscle tone). Other reported symptoms include a weak cry, facial diplegia (paralysis of one part of the body) or paresis (impaired or lack of movement) and mild respiratory distress. A child with TNM typically responds very well to acetylcholinesterase inhibitors. The mothers themselves suffer from exacerbated myasthenia in a third of cases and in those for whom it does worsen, it usually occurs in the first trimester of pregnancy. Signs and symptoms in pregnant mothers tend to improve during the second and third trimester. Complete remission can occur in some mothers.[10] Immunosuppressive therapy should be maintained throughout pregnancy as this reduces the chance of neonatal muscle weakness, as well as controlling the mother's myasthenia.[9]

Very rarely, an infant can be born with arthrogryposis multiplex congenita, secondary to profound intrauterine weakness. This is due to maternal antibodies that target an infant's acetylcholine receptors. In some cases, the mother remains asymptomatic.[9]

[edit] Diagnosis

Myasthenia can be a difficult diagnosis, as the symptoms can be subtle and hard to distinguish from both normal variants and other neurological disorders.[4] A thorough physical examination can reveal easy fatiguability, with the weakness improving after rest and worsening again on repeat of the exertion testing. Applying ice to weak muscle groups characteristically leads to improvement in strength of those muscles. Additional tests are often performed, as mentioned below. Furthermore, a good response to medication can also be considered a sign of autoimmune pathology.

[edit] Physical examination

Muscle fatigability can be tested for many muscles.[11] A thorough investigation includes:

looking upward and sidewards for 30 seconds: ptosis and diplopia. looking at the feet while lying on the back for 60 seconds keeping the arms stretched forward for 60 seconds 10 deep knee bends walking 30 steps on both the toes and the heels 5 situps, lying down and sitting up completely "Peek sign": after complete initial apposition of the lid margins, they quickly

(within 30 seconds) start to separate and the sclera starts to show[4]

[edit] Blood tests

If the diagnosis is suspected, serology can be performed in a blood test to identify certain antibodies:

One test is for antibodies against the acetylcholine receptor.[4] The test has a reasonable sensitivity of 80–96%, but in MG limited to the eye muscles (ocular myasthenia) the test may be negative in up to 50% of the cases.

A proportion of the patients without antibodies against the acetylcholine receptor have antibodies against the MuSK protein.[12]

In specific situations (decreased reflexes which increase on facilitation, co-existing autonomic features, suspected presence of neoplasm, especially of the lung, presence of increment or facilitation on repetitive EMG testing) testing is performed for Lambert-Eaton syndrome, in which other antibodies (against a voltage-gated calcium channel) can be found.

[edit] Neurophysiology

Muscle fibers of patients with MG are easily fatigued, and thus do not respond as well as muscles in healthy individuals to repeated stimulation. By repeatedly stimulating a muscle with electrical impulses, the fatiguability of the muscle can be measured. This is called the repetitive nerve stimulation test. In single fiber electromyography, which is considered to be the most sensitive (although not the most specific) test for MG,[4] a thin needle electrode is inserted into a muscle to record the electric potentials of individual muscle fibers. By finding two muscle fibers belonging to the same motor unit and measuring the temporal variability in their firing patterns (i.e. their 'jitter'), the diagnosis can be made.

[edit] Edrophonium test

Photograph of a patient showing right partial ptosis (left picture). The left lid shows compensatory pseudo lid retraction because of equal innervation of the levator palpabrae superioris (Hering's law of equal innervation). Right picture: after an edrophonium test, note the improvement in ptosis.

The "edrophonium test" is infrequently performed to identify MG; its application is limited to the situation when other investigations do not yield a conclusive diagnosis. This test requires the intravenous administration of edrophonium chloride (Tensilon, Reversol) or neostigmine (Prostigmin), drugs that block the breakdown of acetylcholine by cholinesterase (cholinesterase inhibitors) and temporarily increases the levels of

acetylcholine at the neuromuscular junction. In people with myasthenia gravis involving the eye muscles, edrophonium chloride will briefly relieve weakness.[13]

[edit] Imaging

A chest CT-scan showing a thymoma (red circle).

A chest X-ray is frequently performed; it may point towards alternative diagnoses (e.g. Lambert-Eaton syndrome due to a lung tumor) and comorbidity. It may also identify widening of the mediastinum suggestive of thymoma, but computed tomography (CT) or magnetic resonance imaging (MRI) are more sensitive ways to identify thymomas, and are generally done for this reason.[14]

[edit] Pulmonary function test

Spirometry (lung function testing) may be performed for the assessing of respiratory function if there are concerns about a patient's ability to breathe adequately. The forced vital capacity may be monitored at intervals in order not to miss a gradual worsening of muscular weakness. Acutely, negative inspiratory force (NIF) may be used to determine adequacy of ventilation. Severe myasthenia may cause respiratory failure due to exhaustion of the respiratory muscles.[15]

[edit] Pathological findings

Muscle biopsy is only performed if the diagnosis is in doubt and a muscular condition is suspected. Immunofluorescence shows IgG antibodies on the neuromuscular junction. (Note that it is not the antibody which causes myasthenia gravis that fluoresces, but rather a secondary antibody directed against it.) Muscle electron microscopy shows receptor infolding and loss of the tips of the folds, together with widening of the synaptic clefts. Both these techniques are currently used for research rather than diagnostically.[7]

[edit] Treatment

Treatment is by medication and/or surgery. Medication consists mainly of cholinesterase inhibitors to directly improve muscle function and immunosuppressant drugs to reduce the autoimmune process. Thymectomy is a surgical method to treat MG. For emergency

treatment, plasmapheresis or IVIG can be used as a temporary measure to remove antibodies from the blood circulation.

[edit] Medication

Neostigmine, chemical structure. Acetylcholinesterase inhibitors : neostigmine and pyridostigmine can improve

muscle function by slowing the natural enzyme cholinesterase that degrades acetylcholine in the motor end plate; the neurotransmitter is therefore around longer to stimulate its receptor. Usually doctors will start with a low dose, e.g. 3x20mg pyridostigmine, and increase until the desired result is achieved. If taken 30 minutes before a meal, symptoms will be mild during eating. Side effects, like perspiration and diarrhea can be countered by adding atropine. Pyridostigmine is a short-lived drug with a half-life of about 4 hours.

Azathioprine, chemical structure. Immunosuppressive drugs : prednisone, cyclosporine, mycophenolate mofetil and

azathioprine may be used. It is common for patients to be treated with a

combination of these drugs with a cholinesterase inhibitor. Treatments with some immunosuppressives take weeks to months before effects are noticed. Other immunomodulating substances, such as drugs that prevent acetylcholine receptor modulation by the immune system, are currently being researched.[16]

[edit] Plasmapheresis and IVIG

If the myasthenia is serious (myasthenic crisis), plasmapheresis can be used to remove the putative antibody from the circulation. Also, Intravenous immunoglobulins (IVIG) can be used to bind the circulating antibodies. Both of these treatments have relatively short-lived benefits, typically measured in weeks.[17]

[edit] Surgery

Main article: thymectomy

Thymectomy, the surgical removal of the thymus, is essential in cases of thymoma in view of the potential neoplastic effects of the tumor. However, the procedure is more controversial in patients who do not show thymic abnormalities. Although some of these patients improve following thymectomy, some patients experience severe exacerbations and the highly controversial concept of "therapeutic thymectomy" for patients with thymus hyperplasia is disputed by many experts and efforts are underway to unequivocally answer this important question.

There are a number of surgical approaches to the removal of the thymus gland: transsternal (through the sternum, or breast bone), transcervical (through a small neck incision), and transthoracic (through one or both sides of the chest). The transsternal approach is most common and uses the same length-wise incision through the sternum (breast bone)used for most open-heart surgery. The transcervical approach is a less invasive procedure that allows for removal of the entire thymus gland through a small neck incision. There has been no difference in success in symptom improvement between the transsternal approach and the minimally invasive transcervical approach.[18] However for patients with a thymoma it is important that all the tissue is removed as thymic tissue can regrow. Thymomas can be malignant and are thought to be the onset of other diseases as well. For this reason, many surgeons will only recommend the full sternotomy approach to a thymectomy.

Thymoma is relatively rare in younger (<40) patients, but paradoxically especially younger patients with generalized MG without thymoma benefit from thymectomy. Resection is also indicated for those with a thymoma, but it is less likely to improve the MG symptoms.

[edit] Prognosis

With treatment, patients have a normal life expectancy, except for those with a malignant thymoma (whose lesser life expectancy is on account of the thymoma itself and is

otherwise unrelated to the myasthenia). Quality of life can vary depending on the severity and the cause. The drugs used to control MG either diminish in effectiveness over time (cholinesterase inhibitors) or cause severe side effects of their own (immunosuppressants). A small percentage (around 10%) of MG patients are found to have tumors in their thymus glands, in which case a thymectomy is a very effective treatment with long-term remission. However, most patients need treatment for the remainder of their lives, and their abilities vary greatly. It should be noted that MG is not usually a progressive disease. The symptoms may come and go, but the symptoms do not always get worse as the patient ages. For some, the symptoms decrease after a span of 3–5 years.

[edit] Epidemiology

Myasthenia gravis occurs in all ethnic groups and both genders. It most commonly affects women under 40 - and people from 50 to 70 years old of either sex, but it has been known to occur at any age. Younger patients rarely have thymoma. The prevalence in the United States is estimated at 20 cases per 100,000.[19] Risk factors are the female gender with ages 20 – 40, familial myasthenia gravis, D-penicillamine ingestion (drug induced myasthenia), and having other autoimmune diseases.

Three types of myasthenic symptoms in children can be distinguished:[11]

1. Neonatal: In 12% of the pregnancies with a mother with MG, she passes the antibodies to the infant through the placenta causing neonatal myasthenia gravis. The symptoms will start in the first two days and disappear within a few weeks after birth. With the mother it is not uncommon for the symptoms to even improve during pregnancy, but they might worsen after labor.

2. Congenital: Children of a healthy mother can, very rarely, develop myasthenic symptoms beginning at birth. This is called congenital myasthenic syndrome or CMS. Other than myasthenia gravis, CMS is not caused by an autoimmune process, but due to synaptic malformation, which in turn is caused by genetic mutations. Thus, CMS is a hereditary disease. More than 11 different mutations have been identified and the inheritance pattern is typically autosomal recessive.

3. Juvenile myasthenia gravis: myasthenia occurring in childhood but after the peripartum period.

The congenital myasthenias cause muscle weakness and fatigability similar to those of MG. The symptoms of CMS usually begin within the first two years of life, although in a few forms patients can develop their first symptoms as late as the seventh decade of life. A diagnosis of CMS is suggested by the following:

Onset of symptoms in infancy or childhood. Weakness which increases as muscles tire. A decremental EMG response, on low frequency, of the compound muscle action

potential (CMAP). No anti-AChR or MuSK antibodies.

No response to immunosuppressant therapy. Family history of symptoms which resemble CMS.

The symptoms of CMS can vary from mild to severe. It is also common for patients with the same form, even members of the same family, to be affected to differing degrees. In most forms of CMS weakness does not progress, and in some forms, the symptoms may diminish as the patient gets older. Only rarely do symptoms of CMS become worse with time.

CausesThis section needs additional citations for verification.Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (September 2008)

Thrombotic stroke

In thrombotic stroke a thrombus (blood clot) usually forms around atherosclerotic plaques. Since blockage of the artery is gradual, onset of symptomatic thrombotic strokes is slower. A thrombus itself (even if non-occluding) can lead to an embolic stroke (see below) if the thrombus breaks off, at which point it is called an "embolus." Two types of thrombosis can cause stroke:

Large vessel disease involves the common and internal carotids, vertebral, and the Circle of Willis. Diseases that may form thrombi in the large vessels include (in descending incidence): atherosclerosis, vasoconstriction (tightening of the artery), aortic, carotid or vertebral artery dissection, various inflammatory diseases of the blood vessel wall (Takayasu arteritis, giant cell arteritis, vasculitis), noninflammatory vasculopathy, Moyamoya disease and fibromuscular dysplasia.

Small vessel disease involves the smaller arteries inside the brain: branches of the circle of Willis, middle cerebral artery, stem, and arteries arising from the distal vertebral and basilar artery. Diseases that may form thrombi in the small vessels include (in descending incidence): lipohyalinosis (build-up of fatty hyaline matter in the blood vessel as a result of high blood pressure and aging) and fibrinoid degeneration (stroke involving these vessels are known as lacunar infarcts) and microatheroma (small atherosclerotic plaques).

Sickle cell anemia, which can cause blood cells to clump up and block blood vessels, can also lead to stroke. A stroke is the second leading killer of people under 20 who suffer from sickle-cell anemia.[24]

Embolic stroke

An embolic stroke refers to the blockage of an artery by an arterial embolus, a travelling particle or debris in the arterial bloodstream originating from elsewhere. An embolus is most frequently a thrombus, but it can also be a number of other substances including fat (e.g. from bone marrow in a broken bone), air, cancer cells or clumps of bacteria (usually from infectious endocarditis).

Because an embolus arises from elsewhere, local therapy solves the problem only temporarily. Thus, the source of the embolus must be identified. Because the embolic blockage is sudden in onset, symptoms usually are maximal at start. Also, symptoms may be transient as the embolus is partially resorbed and moves to a different location or dissipates altogether.

Emboli most commonly arise from the heart (especially in atrial fibrillation) but may originate from elsewhere in the arterial tree. In paradoxical embolism, a deep vein thrombosis embolises through an atrial or ventricular septal defect in the heart into the brain.

Cardiac causes can be distinguished between high and low-risk:[25]

High risk: atrial fibrillation and paroxysmal atrial fibrillation, rheumatic disease of the mitral or aortic valve disease, artificial heart valves, known cardiac thrombus of the atrium or ventricle, sick sinus syndrome, sustained atrial flutter, recent myocardial infarction, chronic myocardial infarction together with ejection fraction <28 percent, symptomatic congestive heart failure with ejection fraction <30 percent, dilated cardiomyopathy, Libman-Sacks endocarditis, Marantic endocarditis, infective endocarditis, papillary fibroelastoma, left atrial myxoma and coronary artery bypass graft (CABG) surgery

Low risk/potential: calcification of the annulus (ring) of the mitral valve, patent foramen ovale (PFO), atrial septal aneurysm, atrial septal aneurysm with patent foramen ovale, left ventricular aneurysm without thrombus, isolated left atrial "smoke" on echocardiography (no mitral stenosis or atrial fibrillation), complex atheroma in the ascending aorta or proximal arch

Systemic hypoperfusion

Systemic hypoperfusion is the reduction of blood flow to all parts of the body. It is most commonly due to cardiac pump failure from cardiac arrest or arrhythmias, or from reduced cardiac output as a result of myocardial infarction, pulmonary embolism, pericardial effusion, or bleeding. Hypoxemia (low blood oxygen content) may precipitate the hypoperfusion. Because the reduction in blood flow is global, all parts of the brain may be affected, especially "watershed" areas - border zone regions supplied by the major cerebral arteries. A watershed stroke refers to the condition when blood supply to these areas is compromised. Blood flow to these areas does not necessarily stop, but instead it may lessen to the point where brain damage can occur. This phenomenon is also referred to as "last meadow" to point to the fact that in irrigation the last meadow receives the least amount of water.

Venous thrombosis

Cerebral venous sinus thrombosis leads to stroke due to locally increased venous pressure, which exceeds the pressure generated by the arteries. Infarcts are more likely to

undergo hemorrhagic transformation (leaking of blood into the damaged area) than other types of ischemic stroke.[13]

Intracerebral hemorrhage

It generally occurs in small arteries or arterioles and is commonly due to hypertension, intracranial vascular malformations (including cavernous angiomas or arteriovenous malformations), cerebral amyloid angiopathy, or infarcts into which secondary haemorrhage has occurred.[2] Other potential causes are trauma, bleeding disorders, amyloid angiopathy, illicit drug use (e.g. amphetamines or cocaine). The hematoma enlarges until pressure from surrounding tissue limits its growth, or until it decompresses by emptying into the ventricular system, CSF or the pial surface. A third of intracerebral bleed is into the brain's ventricles. ICH has a mortality rate of 44 percent after 30 days, higher than ischemic stroke or even the very deadly subarachnoid hemorrhage (which, however, also may be classified as a type of stroke[2]).

[edit] Pathophysiology

[edit] Ischemic

This section needs additional citations for verification.Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (September 2008)

Micrograph showing cortical pseudolaminar necrosis, a finding seen in strokes on medical imaging and at autopsy. H&E-LFB stain.

Micrograph of the superficial cerebral cortex showing neuron loss and reactive astrocytes in a person that suffered a stroke. H&E-LFB stain.

Ischemic stroke occurs due to a loss of blood supply to part of the brain, initiating the ischemic cascade.[26] Brain tissue ceases to function if deprived of oxygen for more than 60 to 90 seconds and after approximately three hours, will suffer irreversible injury possibly leading to death of the tissue, i.e., infarction. (This is why TPAs (e.g. Streptokinase, Altapase) are given only until three hours since the onset of the stroke.) Atherosclerosis may disrupt the blood supply by narrowing the lumen of blood vessels leading to a reduction of blood flow, by causing the formation of blood clots within the vessel, or by releasing showers of small emboli through the disintegration of atherosclerotic plaques. Embolic infarction occurs when emboli formed elsewhere in the circulatory system, typically in the heart as a consequence of atrial fibrillation, or in the carotid arteries, break off, enter the cerebral circulation, then lodge in and occlude brain blood vessels. Since blood vessels in the brain are now occluded, the brain becomes low in energy, and thus it resorts into using anaerobic respiration within the region of brain tissue affected by ischemia. Unfortunately, this kind of respiration produces less adenosine triphosphate (ATP) but releases a by-product called lactic acid. Lactic acid is an irritant which could potentially destroy cells since it is an acid and disrupts the normal acid-base balance in the brain. The ischemia area is referred to as the "ischemic penumbra".[27]

Then, as oxygen or glucose becomes depleted in ischemic brain tissue, the production of high energy phosphate compounds such as adenosine triphosphate (ATP) fails, leading to failure of energy-dependent processes (such as ion pumping) necessary for tissue cell survival. This sets off a series of interrelated events that result in cellular injury and death. A major cause of neuronal injury is release of the excitatory neurotransmitter glutamate. The concentration of glutamate outside the cells of the nervous system is normally kept low by so-called uptake carriers, which are powered by the concentration

gradients of ions (mainly Na+) across the cell membrane. However, stroke cuts off the supply of oxygen and glucose which powers the ion pumps maintaining these gradients. As a result the transmembrane ion gradients run down, and glutamate transporters reverse their direction, releasing glutamate into the extracellular space. Glutamate acts on receptors in nerve cells (especially NMDA receptors), producing an influx of calcium which activates enzymes that digest the cells' proteins, lipids and nuclear material. Calcium influx can also lead to the failure of mitochondria, which can lead further toward energy depletion and may trigger cell death due to apoptosis.

Ischemia also induces production of oxygen free radicals and other reactive oxygen species. These react with and damage a number of cellular and extracellular elements. Damage to the blood vessel lining or endothelium is particularly important. In fact, many antioxidant neuroprotectants such as uric acid and NXY-059 work at the level of the endothelium and not in the brain per se. Free radicals also directly initiate elements of the apoptosis cascade by means of redox signaling.[24]

These processes are the same for any type of ischemic tissue and are referred to collectively as the ischemic cascade. However, brain tissue is especially vulnerable to ischemia since it has little respiratory reserve and is completely dependent on aerobic metabolism, unlike most other organs.

Brain tissue survival can be improved to some extent if one or more of these processes is inhibited. Drugs that scavenge reactive oxygen species, inhibit apoptosis, or inhibit excitatory neurotransmitters, for example, have been shown experimentally to reduce tissue injury due to ischemia. Agents that work in this way are referred to as being neuroprotective. Until recently, human clinical trials with neuroprotective agents have failed, with the probable exception of deep barbiturate coma. However, more recently NXY-059, the disulfonyl derivative of the radical-scavenging spintrap phenylbutylnitrone, is reported to be neuroprotective in stroke.[28] This agent appears to work at the level of the blood vessel lining or endothelium. Unfortunately, after producing favorable results in one large-scale clinical trial, a second trial failed to show favorable results.[24]

In addition to injurious effects on brain cells, ischemia and infarction can result in loss of structural integrity of brain tissue and blood vessels, partly through the release of matrix metalloproteases, which are zinc- and calcium-dependent enzymes that break down collagen, hyaluronic acid, and other elements of connective tissue. Other proteases also contribute to this process. The loss of vascular structural integrity results in a breakdown of the protective blood brain barrier that contributes to cerebral edema, which can cause secondary progression of the brain injury.

As is the case with any type of brain injury, the immune system is activated by cerebral infarction and may under some circumstances exacerbate the injury caused by the infarction. Inhibition of the inflammatory response has been shown experimentally to reduce tissue injury due to cerebral infarction, but this has not proved out in clinical studies.

[edit] Hemorrhagic

Head CT showing deep intracerebral hemorrhage due to bleeding within the cerebellum, approximately 30 hours old.

Hemorrhagic strokes result in tissue injury by causing compression of tissue from an expanding hematoma or hematomas. This can distort and injure tissue. In addition, the pressure may lead to a loss of blood supply to affected tissue with resulting infarction, and the blood released by brain hemorrhage appears to have direct toxic effects on brain tissue and vasculature.[24]