Chapter 3: EMG/NCS Flashcards
concentric vs monopolar EMG needles?
- monopolar needles give rise to increased variability of motor unit potentials ,
- monopolar record from larger areas of muscle and produce larger motor unit potentials.
For these reasons, most centers prefer to use concentric needles.
- monopolar needles may cause less pain however.
normal CMAP and absent response with stimulation after trauma suggests?
neuropraxic injury > transection injury, as with transection injury you expect CMAP to be abnormal
increment found with 20Hz fast stim is seen in ?
botulism (less than 100%) and LEMS (>100%)
decrement found with slow stim?
myasthenia, botulism
decreased interference pattern seen on EMG depicts?
neurogenic process
CMT1 vs CMT2A
1 is primary demyelinating and 2A is primary axonal
In a posterior cord lesion to the plexus, which reflexes are abnormal: Biceps, brachialis, triceps
triceps and brachialis, biceps is preserved
most sensitive test to diagnose MG?
single fiber emg of the frontalis muscle
hereditary vs acquired demyelinating polyneuropathies difference on NCS?
Both have prolonged distal latency and reduced conduction velocity, but only acquired have abnormal temporal dispersion.
In patients with neurogenic TOS, which ares of the cord are primarily affected?
medial cord or lower trunk
EMG sign of chronic denervation
MUP with large duration and amplitude
myotonia congenita presents with
channelopathy that presents with myotonia, stiffness and weakness in cold temperatures
What is the earliest diagnostic change in a patient with length dependent axonal polyneuropathy
loss of sural sensory response
amyloid myopathy?
usually caused by hereditary amyloidosis or primary (not common in secondary)
patients can present with peripheral neuropathy and hypertrophic muscles (although still weak)
CK is elevated
EMG/NCS shows combination of neuropathic and myopathic changes
muscle biopsy reveals amyloid deposition
myopathic EMG?
short duration, small amplitude motor units with reduced recruitment
whats considered a normal change in amplitude after 15 seconds of exercise?
<30% inc
repair vs facilitation after stim?
repair: improvement in the junction after brief exercise and therefore improvement in the decrement
Facilitation: significant increase in the CMAP with with exercise.
expected EMG findings in patients with MGA and CTS?
delayed distal latency (because of CTS) + spuriously inc conduction velocity and positive dip on proximal stimulation
How do differentiate a cervical root avulsion from a brachial plexopathy?
Sensory studies should be normal in a cervical root avulsion (only tests to the DRG)
CMAP and conduction velocity in MFS?
normal, as the demyelination is occurring in specialized sensory fibers not tested on NCS
