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EMG and NCS testing
CBN II
36
Medical
Graduate
01/28/2011

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Term
what is EMG?
Definition
electrodiagnostic medicine via percutaneous needle examination (not surface) often used to dx radiculopathy and distal focal entrapment syndrome.
Term
what does the electrodiagnostic consultation consist of?
Definition
hx, exam, EMG/NCS, clinical correlation, and recommendations
Term
what does electrodiagnostic testing only test?
Definition
the LMN (anterior horn cell and distal)
Term
what are NCS used for?
Definition
sensory, motor and mixed - but only large fibers and subject to temperature/height+length/age
Term
what are late responses (type of NCS)? (*exam question*)
Definition
these test the more proximal aspects of the nerve and are the: **H-reflex, which electrically tests the equivalent of the achilles reflex (S1) via the gastroccoleus complex** and the *F-wave, which is obtainable in every muscle: assessing the efferent pathway for plexopathy or AIDP (acute inflammatory demyelinating plexopathy/guillain-barre).
Term
where are needles placed in EMG? how is the muscle evaluated?
Definition
needles are placed in the muscle belly paraspinally and in the limbs and the muscle is evaluated at rest, needle insertion/movement, submaximal contraction and maximal contraction.
Term
what are parameters are evaluated in an EMG?
Definition
waveforms (amplitude, shape, phases, duration, audio quality), firing rate (frequency), and recruitment pattern.
Term
what information is obtained w/EMG?
Definition
chronicity, severity, location and neuropathic vs myopathic
Term
what is repetitive stimulation?
Definition
this type of NCS is used to dx neuromuscular junction disorders (myasthenia, botulism). single fiber EMG can also be used for this purpose.
Term
what is the blink/corneal reflex?
Definition
this tests the afferent CN5 and efferent CN7 fibers by wiping the cornea w/a cotton swab. this is part of the bell's palsy dx which also includes NCS and prognosticates best @ 1 week post-symptom onset.
Term
what are the evoked potentials electrodiagnostic tests? when are they used?
Definition
evoked potential tests: somatosensory, brainstem auditory, visual, and dermatomal. clinical uses: demyelinating disorders (MS), CPA (cerebellopontine angle) tumors, myelopathy, and intraoperative monitoring.
Term
when is EMG testing most commonly used in a clinical setting?
Definition
for symptoms of pain, paresthesia, and weakness
Term
what are the clinical uses of electrodiagnostic testing?
Definition
to confirm clinical suspicion, determine/quantify severity, prognosticate, and r/o concurrent pathology
Term
what kinds of radiculopathy are EMGs used to dx?
Definition
cervical, thoracic (least common), and lumbosacral (most common)
Term
when is the best time do undergo electrodiagnostic testing?
Definition
**3 wks post condition onset (esp w/radiculopathy)
Term
what is a common form of focal neuropathy?
Definition
entrapment syndrome
Term
what is the most common focal entrapment neuropathy? etiology? (*exam question*)
Definition
carpal tunnel - which is due to focal median compression neuropathy at the wrist.
Term
what is the gold standard for carpal tunnel syndrome dx?
Definition
NCS. EMG is optional and may be used to r/o radiculopathy, plexopathy, double crush (prox/distal pathology) etc.
Term
what is the 2nd most common focal entrapment neuropathy?
Definition
focal ulnar neuropathy at the elbow - cubital tunnel syndrome
Term
what is peroneal neuropathy?
Definition
this division of the sciatic nerve usually becomes compressed at the fibular neck (but can also occur at the ankle). clinically this manifests as a foot drop.
Term
what is radial neuropathy?
Definition
"saturday night palsy" - called such due to the association where intoxicated pts would fall asleep on their arm, compressing the radial nerve on the humerus and wake up w/wrist drop.
Term
what is meralgia paresthetica?
Definition
lateral femoral cutaneous neuropathy due to compression by abdominal fat (along w/tightening of belts and cell phone clips) along the lateral femoral cutaneous nerve as it passes by the ASIS. (also sometimes occurs in pregnant women). pts present w/paresthesias in the anterolateral thigh - which may be confused w/radiculopathies (should be in ddx).
Term
what is tarsal tunnel syndrome?
Definition
tibial nerve compression at the ankle due. less common than the carpal variant - this should be on the ddx for refractory plantar fasciitis.
Term
what is long thoracic nerve syndrome?
Definition
this causes scapular winging exacerbated by protraction clinically and is usually due to mastectomy or strenuous overhead activity (volleyball).
Term
what characterizes suprascapular neuropathy?
Definition
pts w/this will present w/chronic shoulder pain and rotator cuff weakness/atrophy - and needs to be differentiated from the much more common rotator cuff tear (sometimes hard to do, b/c as pts age there is some physiologic tearing which may not be the cause of pain). can be due to a ganglion cyst or impingement at the glenoid notch into the infraspinatus.
Term
what are common causes of sciatic neuropathy?
Definition
postoperative (from total hip arthroplasty), trauma - open/closed hip dislocation, mass, or fracture. the sciatic nerve becomes the tibial/peroneal nerve (peroneal nerve division more commonly affected).
Term
why are EMGs helpful in dx of peripheral polyneuropathy?
Definition
they can help classify pathology - whether it be demyelinating, axonal, both, or hereditary/aquired. also what kinds of nerves are affected: sensory, motor, mixed.
Term
can electrodiagnostic testing determine the cause of polyneuropathy?
Definition
no
Term
what are the clinical features of myopathy?
Definition
*proximal weakness (glutes, quads, deltoids, pecs, etc): difficulty w/chairs, steps, and overhead.
Term
what characterizes EMG testing in pts w/myopathy?
Definition
needle EMG testing reveals spontaneous potentials. motor units are small as opposed to the large potentials seen in neuropathy. generally NCS is normal.
Term
are biopsies performed for myopathy?
Definition
yes, and EMG testing should not be performed on areas which area going to be biopsied.
Term
how is an EMG/NCS ordered?
Definition
order to r/o (extension of the clinical evaluation), check b/l?, include previous studies, and list symptoms of concern
Term
what conditions should EMG be used for diagnosing?
Definition
myopathy, neuropathy, motor neuron disease, radiculopathy, and plexopathy
Term
how does electrodiagnostic testing compare to imaging (CT/MRI etc)?
Definition
electrodiagnostic testing assesses nerve *function - not structure (as w/imaging). this makes it a good adjunct to imaging.
Term
when is premedication used for electrodiagnostic testing?
Definition
usually just for children - only a little uncomfortable.
Term
what contraindications exist for electrodiagnostic testing?
Definition
bleeding diathesis, local/systemic infection, pacemaker/defibrillator (relatively safe), and phobia
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