EMG

Question 1

What is EMG?

Answer 1

The recording of electrical activity in muscle

Question 2

What can an EMG show?

Answer 2

It can distinguish myopathic from neurogenic muscle wasting and weakness.

Question 3

What can an EMG find that cannot be seen?

Answer 3

Chronic denervation or fasciculations in clinically normal muscle

Question 4

In what diseases is EMG obligatory?

Answer 4

In motor neurone diseases

Question 5

What can an EMG needle “see”?

Answer 5

Conventional EMG needles record from a hemisphere of radius of about 1 mm. Within this volume there are some 100 muscle fibres.

Question 6

WHat are we analyzing from an EMG?

Answer 6

The waveforms and firing rates of single motor or multiple motor units

Question 7

Eamples of unnormal EMGs

Answer 7

Abnormal spontaneous activity. (A) Fibrillations (*) and positive sharp waves (**) in an acutely denervated hand muscle. (B) Single, doublet, triplet, and multiplet motor unit neuromyotonic discharges. Bursts of discharge are irregular in frequency and the intra-burst frequency of discharge is up to 200 Hz. (C) Fasciculations in the tongue in a patient with amyotrophic lateral sclerosis. The single discharges are irregular and occur on a background of ongoing EMG activity caused by poor relaxation. (D) Myotonic discharges in a patient with dystrophia myotonica. There is a characteristic waxing and waning in frequency.

Question 8

HOw does A recruitment pattern during maximal contraction look in a normal person, spinal muscular atrophy and polymyositis?

Answer 8