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25 Cards in this Set
- Front
- Back
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Why are motor unit recruitment patterns reduced in neuropathic conditions? |
loss of firing of entire motor units |
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What is the earliest an H reflex will be abnormal after the onset of radiculopathy? |
immediately |
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How would lumbosacral disc herniation lead to diminished SNAP amplitude? |
via compression of dorsal root ganglion. There will be no change in SNAP if compressed proximal to DRG. |
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Are motor unit action potentials larger with monopolar or concentric needles? |
monopolar |
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What is a significant side-to-side difference fo the H reflex? |
1.5ms. |
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How does repetitive nerve stimulation at rates of 20 to 50 per second have a facilitating effect on end-plate potential amplitudes? |
calcium accumulation in the nerve terminal. |
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In a patient with suspected myasthenia gravis, repetitive nerve stimulation at 3 per is performed on the right ulnar n. A 5% decrement is noted before exercise which reverts to no decrement after exercise. What is the next step in electrodiagnostic process? |
Repetitive stimulation of a more proximal nerve (Decrements of up to 10% are normal) |
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Which branch of the median n. is most likely to be affected in a Martin-Gruber anastomosis? |
Anterior interroseus nerve (so usually only affects motor fibers) |
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Which muscles are innervated by the anterior interosseus nerve? |
PQ, FPL, FDP |
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Which nerve is most commonly involved in parsonage turner syndrome? |
Long thoracic nerve. |
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How is Lambert Eaton Syndrome distinguished from myasthenia gravis on EMG? |
LE has postexercise facilitation >200% of the CMAP amplitude. The facilitation in MG is much smaller. |
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Corticosteroids cause this type of fiber atrophy |
type II |
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What is typically seen on EMG of patients with steroid myopathy? |
The test is typically normal. Steroid myopathy preferentially affects type II fibers which are recruited only with maximal effort. By then the interference pattern is too full to detect changes in amplitude or duration. Positive sharp waves and fibs are not present |
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percentage of of motor units expected to polyphasic with monopolar needles |
30% |
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percentages of motor units expected to polyphasic with concentric needles |
15% |
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List all muscles innervated by superficial peroneal nerve |
peroneus longus and brevis
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Peroneal nerve at the ankle lies between what 2 tendons |
tibialis anterior and EHL |
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What is resting membrane potential? |
-90mV |
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How is amplitude measured for CMAP? for SNAP? |
CMAP: baseline to peak SNAP: peak to peak |
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What is temporal dispersion? |
Relative desynchronization of compound action potential due to different rates of conduction of each synchronously evoked potential from the stimulation point to the recording electrode (if physiologic area under the curve should not change). |
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What is conduction block? |
Failure of an action potential to be conducted past a certain point whereas conduction is possible below the point of the block. |
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What can account for a positive dip on a CMAP? |
Active electrode off muscle belly Martin Gruber in setting of CTS Pseudopositive secondary to stimulating SNAP |
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What is the utility of the F wave? |
1. Eval for demyelinating peripheral neuropathy 2. Plexopathy eval 3. Early GBS 4. Proximal focal mononeuropathy |
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How is an H wave different than a F wave? |
F wave is usually 3-5% of M wave, but H reflex can be higher than M wave. F wave has variable latency and configuration, but H wave is consistent with a given stimulus F wave is usually polyphasic while H wave is usually triphasic. F wave can be elicited from any muscle. H wave from gastrocs and FCR F wave uses supramaximal stim, H wave submax/long stim |
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What is an A wave? |
Axon reflex - due to normal or pathologic axon branching that is a richocet of the actional potential off a proximal axonal point seen sometimes when recording F waves. Occurs before F response and is identical in latency and configuration with each successive stimulation. |
