NEUROMUSCULAR DISEASES LEADING TO RESPIRATORY INSUFFICIENCY
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Neuromuscular disorders can lead to respiratory insufficiency mainly due to the affection of respiratory muscles, namely upper airway muscles, respiratory accessory muscles, diaphragm and even abdominal muscles. However, mechanisms other than respiratory muscle involvement, such as alteration of mechanical properties of respiratory apparatus (i.e. scoliosis), appearance of muscle fatigue, alterations in the control of ventilation, dysfunction of the upper airway, involvement of heart muscle may also contribute to respiratory problems during the course of the neuromuscular disorders. Neuromuscular structures which promote problems in respiration when involved are related motor neurons, peripheral nerves-mainly phrenic nerve-, related nerve- muscle junctions and respiratory muscles themselves. In this report, neuromuscular diseases of these structures will be presented. Among motor neuron diseases, “poliomyelitis” has been eradicated after the employment of its specific vaccination. “Amyotrophic lateral sclerosis (ALS)” is a degenerative disease of all motor neurons, which progress in few years to death due to respiratory insufficiency. When bulbar involvement occurs, it usually presents with swallowing difficulties, which may cause aspiration. Respiratory involvement appears later in the course, which urges ventilatory support. One of the emergency medicine topics is “acute inflammatory demyelinating neuropathy (AIDP), i.e. Guillain Barre syndrome (GBS)”. This neuropathy causes muscle weakness as well as sensory impairment due to drop out of peripheral nerves, which is caused by an immunological attack. Progression limits itself in 4 weeks. If progression reaches to respiratory muscles, which is a frequent state after cranial nerve involvement, intensive care conditions are needed. Disease has a plateau for several weeks, after which it regresses. Therefore, ventilatory support and prevention from infections at this time is life saving. Other neuropathies, which cause respiratory problems much less frequently, are the phrenic nerve involvement during “chronic inflammatory demyelinating neuropathy (CIDP)”, a form of hereditary neuropathy “Charcot Marie Tooth disease (CMT)” which affects
phrenic nerve, “Churg-Strauss disease” in which asthmatic respiratory disease is evident. One of the most important disease groups which alter respiration are the diseases of neuromuscular junction, “Myasthenia gravis (MG)” being the most important and most frequent. Myasthenia gravis is the autoimmune disease of nicotinic acetyl choline receptors (AchR) at the post synaptic membrane of nerve-muscle junction. Patients usually present with asymmetrical ptosis and/or diplopia, bulbar symptoms such as chewing, speech and swallowing difficulties, and generalized fatigue. Complaints fluctuate during the day. If the respiratory muscles are involved, myasthenic crisis is apparent. This is an emergency problem and one cannot see the fluctuation during the day in this fulminating clinical picture. The disease can worsen by infections, pregnancy, puerperal period, and by some medicines. Resting restores the lost functions by the recovery of muscle strength. Although main treatment regimen has to comprise immune suppressive medication, symptomatic period necessitates symptomatic anti- cholinesterase therapy. The dose of anti-cholinesterase medication has to be adjusted due to symptom intensity and on patient basis. Although it is life saving in most occasions, excessive anti-cholinesterases themselves cause muscle weakness and they also augment bronchial secretion. Respiratory problems in MG occur due to several reasons: When swallowing difficulties are evident, aspiration and its consequences are the main problem. Anti-cholinesterase treatment can be another problem with augmented production of bronchial secretion. This is especially an enigma when there is critical respiratory muscle involvement. The scenario then, is the increased bronchial secretion, effort to cough with already weak muscles and further fatigue during the process and become increasingly unable to expectorate after each effort. A vicious circle is evident and is usually amplified by the superimposed infections. Respiratory insufficiency at any point of this vicious circle has to be expected and patient has to be secured in terms of respiration as soon as possible. Another neuromuscular junction disease “Lambert- Eaton myasthenic syndrome (LEMS)” can also lead to respiratory problems due to muscle fatigue as well as
NEUROMUSCULAR DISEASES LEADING TO RESPIRATORY INSUFFICIENCY
Piraye SERDARO⁄LU
‹stanbul Üniversitesi ‹stanbul T›p Fakültesi, Nöroloji Anabilim Dal›, ‹STANBUL.
322
small cell carcinoma of lung, which is a frequently associated condition. The toxic neuromuscular disease, “botulismus” is another condition, which usually urges intensive ventilatory support. Myopathies, in which the main damage is in muscle fiber itself, are the main neuromuscular causes of respiratory insufficiency. In inflammatory myopathies, direct involvement of respiratory muscles is rare. However, interstitial lung disease, which may accompany, especially Jo-1 myositis can cause mild respiratory problem. The end stage of other hereditary myopathies of dystrophic, structural or metabolic origin is usually respiratory insufficiency. The diminishing respiratory function can be the result of frequent development of scoliosis or other chest deformities. Cardiomyopathy, which might accompany the existing myopathy can be another cause of breathing problems. At the end stage of any muscle disease, the weakness of respiratory muscles limits coughing and causes frequent lung infections which in turn can urge assisted ventilation. However, some myopathies frequently and selectively involve respiratory muscles. “Adult onset
Pompe disease” for example, can present with respiratory insufficiency, even before the weakness in extremities. Some “congenital myopathies” such as multicore disease, desmin myopathies, rod myopathy, or some “metabolic myopathies” such as debrancher enzyme defect, some mitochondrial myopathies are other examples. In “myotonic dystrophy (DM)” patients usually experience chronic hypo-ventilation. One specific myopathy of interest is “critical care myopathy or myosin loss myopathy”. This myopathy developes in patients who had been intubated and stayed in the intensive care unit. It is usually comes into attention when the patient cannot be weaned from the respirator. Patient is also quadriplegic. Sepsis, high dose corticosteroids, non- depolarizing blocking agents are thought to be the underlying causes, solely or in combination. If these conditions are reversed, the disease is self limited. Respiratory muscle training, starting from the onset of the disease is important. However, the physician has to be careful about the fatigue generating conditions such as myasthenia gravis or metabolic diseases, in which normal training pattern may be harmful.
P SERDARO⁄LU
Neuromuscular disorders can lead to respiratory insufficiency mainly due to the affection of respiratory muscles, namely upper airway muscles, respiratory accessory muscles, diaphragm and even abdominal muscles. However, mechanisms other than respiratory muscle involvement, such as alteration of mechanical properties of respiratory apparatus (i.e. scoliosis), appearance of muscle fatigue, alterations in the control of ventilation, dysfunction of the upper airway, involvement of heart muscle may also contribute to respiratory problems during the course of the neuromuscular disorders. Neuromuscular structures which promote problems in respiration when involved are related motor neurons, peripheral nerves-mainly phrenic nerve-, related nerve- muscle junctions and respiratory muscles themselves. In this report, neuromuscular diseases of these structures will be presented. Among motor neuron diseases, “poliomyelitis” has been eradicated after the employment of its specific vaccination. “Amyotrophic lateral sclerosis (ALS)” is a degenerative disease of all motor neurons, which progress in few years to death due to respiratory insufficiency. When bulbar involvement occurs, it usually presents with swallowing difficulties, which may cause aspiration. Respiratory involvement appears later in the course, which urges ventilatory support. One of the emergency medicine topics is “acute inflammatory demyelinating neuropathy (AIDP), i.e. Guillain Barre syndrome (GBS)”. This neuropathy causes muscle weakness as well as sensory impairment due to drop out of peripheral nerves, which is caused by an immunological attack. Progression limits itself in 4 weeks. If progression reaches to respiratory muscles, which is a frequent state after cranial nerve involvement, intensive care conditions are needed. Disease has a plateau for several weeks, after which it regresses. Therefore, ventilatory support and prevention from infections at this time is life saving. Other neuropathies, which cause respiratory problems much less frequently, are the phrenic nerve involvement during “chronic inflammatory demyelinating neuropathy (CIDP)”, a form of hereditary neuropathy “Charcot Marie Tooth disease (CMT)” which affects
phrenic nerve, “Churg-Strauss disease” in which asthmatic respiratory disease is evident. One of the most important disease groups which alter respiration are the diseases of neuromuscular junction, “Myasthenia gravis (MG)” being the most important and most frequent. Myasthenia gravis is the autoimmune disease of nicotinic acetyl choline receptors (AchR) at the post synaptic membrane of nerve-muscle junction. Patients usually present with asymmetrical ptosis and/or diplopia, bulbar symptoms such as chewing, speech and swallowing difficulties, and generalized fatigue. Complaints fluctuate during the day. If the respiratory muscles are involved, myasthenic crisis is apparent. This is an emergency problem and one cannot see the fluctuation during the day in this fulminating clinical picture. The disease can worsen by infections, pregnancy, puerperal period, and by some medicines. Resting restores the lost functions by the recovery of muscle strength. Although main treatment regimen has to comprise immune suppressive medication, symptomatic period necessitates symptomatic anti- cholinesterase therapy. The dose of anti-cholinesterase medication has to be adjusted due to symptom intensity and on patient basis. Although it is life saving in most occasions, excessive anti-cholinesterases themselves cause muscle weakness and they also augment bronchial secretion. Respiratory problems in MG occur due to several reasons: When swallowing difficulties are evident, aspiration and its consequences are the main problem. Anti-cholinesterase treatment can be another problem with augmented production of bronchial secretion. This is especially an enigma when there is critical respiratory muscle involvement. The scenario then, is the increased bronchial secretion, effort to cough with already weak muscles and further fatigue during the process and become increasingly unable to expectorate after each effort. A vicious circle is evident and is usually amplified by the superimposed infections. Respiratory insufficiency at any point of this vicious circle has to be expected and patient has to be secured in terms of respiration as soon as possible. Another neuromuscular junction disease “Lambert- Eaton myasthenic syndrome (LEMS)” can also lead to respiratory problems due to muscle fatigue as well as
NEUROMUSCULAR DISEASES LEADING TO RESPIRATORY INSUFFICIENCY
Piraye SERDARO⁄LU
‹stanbul Üniversitesi ‹stanbul T›p Fakültesi, Nöroloji Anabilim Dal›, ‹STANBUL.
322
small cell carcinoma of lung, which is a frequently associated condition. The toxic neuromuscular disease, “botulismus” is another condition, which usually urges intensive ventilatory support. Myopathies, in which the main damage is in muscle fiber itself, are the main neuromuscular causes of respiratory insufficiency. In inflammatory myopathies, direct involvement of respiratory muscles is rare. However, interstitial lung disease, which may accompany, especially Jo-1 myositis can cause mild respiratory problem. The end stage of other hereditary myopathies of dystrophic, structural or metabolic origin is usually respiratory insufficiency. The diminishing respiratory function can be the result of frequent development of scoliosis or other chest deformities. Cardiomyopathy, which might accompany the existing myopathy can be another cause of breathing problems. At the end stage of any muscle disease, the weakness of respiratory muscles limits coughing and causes frequent lung infections which in turn can urge assisted ventilation. However, some myopathies frequently and selectively involve respiratory muscles. “Adult onset
Pompe disease” for example, can present with respiratory insufficiency, even before the weakness in extremities. Some “congenital myopathies” such as multicore disease, desmin myopathies, rod myopathy, or some “metabolic myopathies” such as debrancher enzyme defect, some mitochondrial myopathies are other examples. In “myotonic dystrophy (DM)” patients usually experience chronic hypo-ventilation. One specific myopathy of interest is “critical care myopathy or myosin loss myopathy”. This myopathy developes in patients who had been intubated and stayed in the intensive care unit. It is usually comes into attention when the patient cannot be weaned from the respirator. Patient is also quadriplegic. Sepsis, high dose corticosteroids, non- depolarizing blocking agents are thought to be the underlying causes, solely or in combination. If these conditions are reversed, the disease is self limited. Respiratory muscle training, starting from the onset of the disease is important. However, the physician has to be careful about the fatigue generating conditions such as myasthenia gravis or metabolic diseases, in which normal training pattern may be harmful.
P SERDARO⁄LU
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