14: Basic EMG and Analysis of Spontaneous Activity

Question 1

What spontaneous activity originates from the motor neuron/axon?

Answer 1

Fascic; myokymia; tetany; cramp; neuromyotonia

Question 2

What spontaneous activity originates from the NMJ?

Answer 2

Endplate noise

Question 3

What spontaneous activity originates from the terminal axon?

Answer 3

Endplate spike

Question 4

What spontaneous activity originates from the muscle fiber?

Answer 4

PSW; fib; myotonia

Question 5

What spontaneous activity originates from multiple muscle fibers?

Answer 5

CRD

Question 6

Duration and amplitude of end-plate spike?

Answer 6

1-5 ms; 10-100 uV

Question 7

Firing rate of PSW’s and fibs? Duration of fibs?

Answer 7

.5 - 10 Hz;
1-5 ms

Question 8

What indicates increased insertional activity?

Answer 8

Waveform generated other than endplate potentials lasting longer than 300 ms

Question 9

Firing rate of myotonic discharge? Neuromyotonia? CRD?

Answer 9

20-150 Hz;
150-250 Hz;
5-100 Hz

Question 10

When can you see 4+ fibrillations?

Answer 10

Trauma (nerve laceration) and infarction (vasculitis)

Question 11

How do CRD’s come about?

Answer 11

Pacemaker muscle fiber; ephatic spread to adjacent denervated fibers; denervation followed by reinnervation followed by denervation again

Question 12

Where can myotonic discharges be seen?

Answer 12

Myotonic dystrophy;
Myotonia congenita;
Paramyotonia congenita;
Hyperkalemic periodic paralysis, polymyositis, acid maltase deficiency, myotubular myopathy

Question 13

When can fasciculations be seen?

Answer 13

MND;
Benign Fasciculation Syndrome;
Radic, polyneuropathy, entrapment neuropathy

Question 14

When are doublets, triplets, and multiplets classically seen?

Answer 14

Tetany from hypocalcemia (distal muscles affected; carpopedal spasm)

Question 15

Firing frequency of myokymic discharges? What can produce them?

Answer 15

5-60 Hz;
radiation, GBS, MS, pontine tumors, hypocalcemia, timber rattlesnake venom;
can see with nerve entrapments, CIDP, radic

Question 16

Freq of cramp potentials?

Answer 16

40-75 Hz

Question 17

When are neuromyotonic discharges seen? Underlying pathology?

Answer 17

Myasthenia, thymoma, malignancy, inflamm demyelinating polyneuropathy (TIMM);
autoimmune channelopathy, with target antigen being peripheral nerve voltage-gated K channel