EEG, NCS, EMG

Question 1

What are PLED’s?

Answer 1

periodic lateralizing epileptiform discharges (PLEDs): may occur with any acute focal cerebral insult (e.g. herpes simplex encephalitis (HSE), abscess, tumor, embolic infarct): seen in 85% of cases of HSE (onset 2–5 d after presentation), if bilateral is ≈ diagnostic of HSE

Question 2

What is SSPE?

Answer 2

Subacute sclerosing panencephalitis (pathognomonic pattern): periodic high voltage with 4–15 secs separation with accompanying body jerks, no change with painful stimulation (differential diagnosis includes PCP overdose)

Question 3

What EEG pattern is seen in CJD?

Answer 3

bilateral sharp wave 1.5–2 per second (early → slowing; later→ triphasic). May resemble PLEDs, but are reactive to painful stimulation (most PLEDs are not)

Question 4

What frequency are alpha waves?

Answer 4

8-13Hz

Question 5

What frequency are theta waves?

Answer 5

4-7Hz

Question 6

What frequency are delta waves?

Answer 6

0-3Hz

Question 7

What frequency are Beta waves?

Answer 7

> 13Hz

Question 8

What do you look for on EEG to confirm burst suppression?

Answer 8

Bursts of 8–12 Hz electrical activity (lasting 1–10 s) that diminish to 1–4 Hz prior to intervals of electrical silence (no excursions ≥ 5 microvolts, lasting > 10 s)

Question 9

What would an increased latency on BAER between I and III suggest?

Answer 9

Lesion between Pons and colliculus - (Vestibular schwannoma)

Question 10

What would and increased latency on BAER between III and V suggest?

Answer 10

Lesion between lower pons and midbrain - (MS)

Question 11

Can a patient having intra-op SSEPs be paralysed?

Answer 11

Yes - reduces muscle artefact but will be unable to see a visible twitch that confirms the stimulus is being received.

Question 12

What are the contraindications to MEP monitoring?

Answer 12

history of epilepsy/seizures
past surgical skull defects
metal in head or neck
use special care with implanted electronic devices

Question 13

When would you be concerned with changes in EP?

Answer 13

Any of the following:

SSEP:
50% decrease in peak signal amplitude from baseline
increase in peak latency > 10%
complete loss of a waveform
TCMEP: sustained 50% decrease in signal amplitude
DEP: decrease in signal of > 60%

Question 14

What is the Stagnara wake up test?

Answer 14

An intraoperative test of voluntary motor function during spine surgery. - described in a publication dated 1973!

Question 15

What are fasciculation potentials typically associated with?

Answer 15

MND

Question 16

What spontaneous activity is seen on EMG following nerve or muscle injury?

Answer 16

positive sharp waves (PSW)

fibrillation potentials (AKA fibrillations or fibs): action potentials arising from single muscle fibers. Detectable on EMG; not visible to the naked eye, c.f. fasciculations. Earliest onset 7–10 days after denervation, sometimes not for 3–4 weeks. If the nerve recovers, it may reinnervate the muscle, but with larger motor units resulting in longer duration and decreased numbers
myotonic discharges (“dive bomber” sound on speaker monitor)

complex repetitive discharge (CRD): ephaptic conduction of groups of adjacent muscle fibers. Occurs in neuropathic or myopathic disorders

Question 17

What is a SNAP?

Answer 17

Sensory nerve action potential. Will be reduced with lesions distal to the sensory ganglion, which is at the level of the neural foramen. i.e. compression proximal to the ganglion (posterolateral disc prolapse for example) will have a normal SNAP.

Question 18

What is the F-wave?

Answer 18

Stimulation of a nerve causes antidromic and orthodromic conduction. Some anterior horn cells that are stimulated antidromically will fire orthodromically, producing an F-wave. Prolonged F-wave latency may occur in multilevel radiculopathy, F-wave latency is also useful to assess proximal root slowing (e.g. GBS)

Question 19

What is the H-reflex?

Answer 19

practical ≈ only in S1 nerve root, similar information to the ankle jerk. Stimulation of Ia afferent fibers passes through a monosynaptic connection causing an orthodromic alpha-motor action potential that can be measured in the triceps surae.

Question 20

How long does it take to develop acute changes on EMG?

Answer 20

around 3 weeks!

Question 21

What EMG findings would you expect to see in radiculopathy?

Answer 21

Fibrillations and/or positive sharp waves in at lease t muscles innervated by a single nerve root in question, but by 2 different peripheral nerves.

abnormal paraspinals (although this will be normal in approx 50%

Question 22

What are the EMG findings in nerve root avulsion?

Answer 22

Motor and sensory signs on examination but normal SNAP.