Nerve Conduction and EMG

Question 1

What are the indications for NCS and EMG?

Answer 1

Aid in the diagnosis of peripheral nerve disease NCS distinguish axonal vs demyelination, EMG diagnose muscle vs nerve.

Question 2

What are F wave latencies

Answer 2

F waves are produced by backfiring along a motor neuron due to supramaximal stimulation. F wave latencies represent proximal demyelination which may otherwise be missed.

Question 3

What are the NCS findings consistent with axonal damage?

Answer 3

Decreased amplitude, normal conduction velocity. Fibrillations on EMG.

Question 4

What are the NCS findings consistent with demyelination?

Answer 4

Partial motor nerve conduction block Reduced motor nerve conduction velocity Normal amplitude. Prolonged distal motor latencies Prolonged F wave latencies

Question 5

What are the EMG findings for nerve disease

Answer 5

Large motor units, decreased recruitment

Question 6

What are the EMG findings for motor unit disease

Answer 6

Small motor units, early recruitments, decreased amplitude and shorter duration

Question 7

Answer 7

Hereditary neuropathy with susceptibility to pressure palsies occurs from deletion of one copy of the PMP 22 gene

Question 9

Answer 9

CIDP

Discussion:

Nerve conduction studies with temporal dispersion, conduction block, and slow conduction are seen in chronic inflammatory
demyelinating polyneuropathy. In Charcot-Marie-Tooth disease, there are slow latencies and nerve conduction velocities, but no

temporal dispersion or block. In amyotrophic lateral sclerosis, nerve conduction studies may be normal or with decreased
compound muscle action potential amplitudes. Nerve conduction studies are normal in fascioscapulohumeral dystrophy and

myasthenia gravis.