Electrodiagnosis for medical student 2017

Pariya Wimonwattrawatee, MD.

Electrodiagnosis

• Electro + Diagnosis

• Nerve conduction studies

• Needle electromyography (EMG) studies

• Evoked potentials (EPs)

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Nerve Conduction Studies (NCS)

• Stimulate the nerves

How fast & how well

the nerve responded

• Motor & sensory

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Axonal Neuropathy

Pariya Wimonwattrawatee, MD.

Demyelination

Pariya Wimonwattrawatee, MD.

Conduction Block

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Physiological Factors Affecting Nerve Conduction

• Age: <5, >50 yo

• Temperature

– UE: 32oC

– LE: 30oC

• Location: proximal / distal

• Nerve size

• Height

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Electromyography (EMG)

EMG vs NCS

• Use a needle

• Not use any electrical shocks

• Direct information about the muscles & indirect information about the nerves

– Inflammatory myopathy

– Axonopathy

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

• Insertional activities

• Spontaneous activities

• Motor unit action potentials

• Recruitment pattern

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Spontaneous activities

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Motor Unit

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Pariya Wimonwattrawatee, MD.

Nerve Injury

• Wallerian degeneration

– Sensory and motor electrical responses similarly remain normal

– Several days – weeks

Pariya Wimonwattrawatee, MD.

Day 1 after a Lesion

• NCS:

– Distal to the lesion: not changed

– Proximal to the lesion: small-amplitude or absent response

• EMG:

– Severe: reduced or discrete recruitment

– Mild: normal

Pariya Wimonwattrawatee, MD.

Days 7 to 10

• Wallerian degeneration

• Complete lesion: SNAPs will be absent

• Incomplete lesions: less marked changes

• Distinguish a neurapraxicinjury from an axon loss lesion

Pariya Wimonwattrawatee, MD.

Days 14 to 21

• Needle EMG:

– Increased insertional activities

– Fibrillation potentials & positive sharp waves in proximal muscles

• Persistent for several months to several years

– Not forever

Pariya Wimonwattrawatee, MD.

Reinnervation

• Axonal regrowth

• Axonal sprouting

Pariya Wimonwattrawatee, MD.

Axonal Regrowth

• 1 mm/day or 1 inch/month

• Short-duration, small-amplitude potentials (nascent potentials)

• Become larger, more polyphasic & longer in duration

Pariya Wimonwattrawatee, MD.

Axonal Sprouting

• Polyphasicity & increased duration

• large-amplitude, long-duration MUAPs

• Usually persist indefinitely

Pariya Wimonwattrawatee, MD.

Advantage of EDx

• Diagnosis– Structure / function

• Pathology– Axon / myelin

– AHC / nerve (motor, sensory) / NMJ

• Degree– Mild / moderate / severe

– Neurapraxia / axonotmesis

Pariya Wimonwattrawatee, MD.

• Localize the lesion

• Determine treatment

• Disease progression

• Provide information about the prognosis

Pariya Wimonwattrawatee, MD.

• WHEN?

• WHY?

• Further physical examination

Pariya Wimonwattrawatee, MD.