Audio
Your concentric needle in a patients EIP and you hear this sound. What is this noise and what does it mean?
(ignore the other intermittent potentials)
Miniature End Plate Potentials (MEPPs) AKA seashell sound. Caused by spontaneous random releases of Ach at the NMJ, you hear it when the needle is close to an endplate
You get a referral for an EDX for carpal tunnel syndrome. Before trying to beat the record of 5 minutes for a CTS evaluation you ask the patient if they have had any EDX studies done before and they say they have had many throughout their life. They report prior distinct episodes of CTS, fibular neuropathy, and cubital tunnel syndrome. Aside from completing the test, what else would you consider ordering?
Consider evaluation for Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) - can consider genetic testing for PMP22 (deletions)
HNPP - transient mononeuropathies are common compression sites. Really just have to keep on the ddx since the individual mononeuropathies are pretty common. No curative treatment but need to be extra careful about compression. AD inheritance
What single radicular level is involved?
NCS: normal upper extremity routines
EMG:
> FDI: decreased recruitment, 4+ fibs
> EIP: decreased recruitment, 4+ fibs
> PT: normal
> Biceps: normal
> Triceps: decreased recruitment, 4+ fibs
> Deltoid: normal
> APB: decreased recruitment, 4+ fibs
>
C8 radiculopathy
Demyelination would most likely cause what affects to the following NCS parameters?
>amplitude
>distal latency
>temporal dispersion
>conduction velocity
amplitude: unchanged
distal latency: prolonged
temporal dispersion/duration: prolonged
Conduction velocity: decreased
What muscle fiber type does steroid myopathy most commonly affect?
A. Type III fibers
B. Type I and II fibers
C. Type II fibers
D. Type I fibers
> get to go again if you can explain to the PGY2's why this is relevant for EMGs?
C. type II fibers (fast-twitch, glycolytic)
EMGs evaluate type I fibers (oxidative) the best. Hence it's not uncommon for someone with steroid myopathy to have a normal EMG. Technically you can test type II fibers but they tend to recruit last and at that point your screen is already filled with MUAPs
Dr. Wongs concentric needle is in a patients APB at rest and he hear the following. His visiting pre-med student asks Dr. Wong what he is hearing, what does he say?
Fibs and PSWs
Bonus: Dr. AOA Healing Hands Stroke Attending Wongs team gets to go next
During an evaluation for ALS/MND. If you could only pick cervical, thoracic or lumbar paraspinals to test with the needle, which one would help you most with making a diagnosis?
Thoracic paraspinals
Essentially thoracic radiculopathies are really rare so if you get spontaneous activity it can help you put together a picture for ALS/MND
In Erb's palsy which of the following EMG/NCS findings are mostly likely to be abnormal?
A. MAC SNAP
B. Digit 1 SNAP
C. LAC SNAP
D. Recruitment of the EIP
C. abnormal LAC nerve SNAP
Erbs palsy = C5-6/upper trunk brachial plexopathy often from head pulling during delivery or stretch injuries of the neck (motorcycle crashes).
What is the earliest evidence of GBS on EDX?
A. Prolonged M wave
B. Prolonged A wave
C. Prolonged F wave
D. Prolonged H reflex
C. Prolonged F wave
what is the anatomical difference between neurapraxia, neurotmesis, and axonotmesis?
neurapraxia: temporary blockage of nerve conduction but axon still intact
axonotmesis: axon injured but epineurium still intact
neurotmesis: axon injured and epineurium disrupted
You just finished testing for spontaneous activity and you ask the patient to give you a little resistance and you get the following finding. What would you classify this finding as?
Myopathic discharges (hard to tell just from video, more obvious when you can actually judge a patients resistance)
You can't make the diagnosis with just this test. Both myasthenia gravis and LEMS will have a decrement on the 2 Hz (slow) RNS.
You would need to do a post-exercise or high rate (10-50 Hz) RNS to distinguish between MG and LEMS. Both of them will show a CMAP increase but the CMAP increase will be huge for LEMS.
Bonus: Dr. Ajoku's team gets to go again
What are the 3 possible locations of the lesion?
Pt presents with hand numbness
NCS: decreased amplitude of digit 2 SNAP. Normal digit 5 SNAP. Reduced amplitude of APB CMAP diffusely
EMG: 1+ fibs in APB and FCR. Normal deltoid, biceps, FCU, FDI, and cervical paraspinals
1. under pronator teres muscle
2. under bicipital aponeurosis
3. under ligament of struthers.
Ulnar neuropathies can occur between the 2 heads of the FCU or under the Arcade of struthers
What is the optimal temperatures of the upper and lower limb for a NCS?
Upper: 32*C
Lower: 30*C
60 year old female with proximal hip and shoulder weakness, periorbital erythematous rash, and erythematous papules over her MCP and IP joints gets an EMG. What EMG findings are you most likely to find?
A. decreased SNAP amplitude
B. Giant MUAPs
C. Decreased recruitment
D. Early/increased recruitment
> If you can explain why this finding occurs to the PGY2's you get to go again!
D. Early/increased recruitment => myopathic disease
myopathy = damaged/weaker muscle fibers -> in order to get same level of contraction as a normal muscle you need to activate more motor units sooner
Your needle is in a patients FDI when you hear this sound. What diagnosis is it classically associated with?
Myotonic discharges aka Divebomber => myotonia
What genetic diseases are caused by the following?
> duplication of PMP-22
> deletion of PMP-22
> mutation of SMN-1
>duplication of PMP-22 = CMT 1A
>deletion of PMP-22 = Hereditary neuropathy with liability to pressure palsy
>mutation of SMN-1 = spinal muscular atrophy
Draw the Brachial Plexus (include as much detail as you can)
The other teams will judge completeness
picture
An EMG potential is considered polyphasic if it crosses the baseline a minimum of how many times?
5 times
Phases = # of baseline crossings + 1
So polyphasia has at least 5 phases (4+1)
Dr. Smeding is doing an ADM motor nerve conduction study. She gets a normal CMAP amplitude when stimulating at the wrist site, but when she tests the below elbow site she notices a 25% decrement in amplitude. Her visiting pre-med asks her whats wrong with the patient. What does Dr. Smeding do next?
Stimulate at the median nerve proximal and distal sites to check for a Martin Gruber anastomosis. Much more likely to have an MGA than an ulnar conduction block in the forearm.
Bonus: if you got it right Dr. Smeding's team goes next
You find yourself with a needle in a patients biceps and you hear the following. What are you hearing and what classic diagnosis is it associated with?
Myokymia aka marching soldiers -> Radiation induced plexopathy
You get a referral for a motor neuron disease EMG evaluation. Patient reports diffuse weakness, especially with smiling and lifting his arms. While performing the needle studies you find short duration, low amplitude and polyphasic waveforms and intermittent fibs and PSW in the triceps, serratus anterior, and pecs.
What is the most likely diagnosis?
Facioscapulohumeral Dystrophy - a specific form of muscular dystrophy that often specifically involves the face and shoulder girdle.
Note: primarily describes myopathic findings but long term myopathy can cause some neuropathic changes
What following would be abnormal in a nerve compression by the Arcade of Frohse?
SNAP: digit 2, digit 5, radial sensory
CMAP: APB, ADM
EMG: FDI, EIP, PT, Brachioradialis, Triceps, Deltoid, paraspinals
Abnormal EIP emg only
Arcade of Frohse = PINopathy -> pure motor neuropathy so SNAPs would be normal. Pretty rare to actually end up testing radial CMAPs so have to have some suspicion to do this test. Brachioradialis not PIN innervated
Dr. Manhas is doing a LESI on Dr. Peterson. To keep his mind off the big needle Dr. Peterson asks Dr. Manhas to explain the detailed anatomy of the nuclei involved in the blink reflex. What does Dr. Manhas say?
(answer includes the different nuclei, nerves, and R1 vs R2)
1. Afferent signal via CNV -> Vs (medulla) -> ipsilateral CNVII + ipsilateral Vm (pons).
2. Ipsilateral CNVII -> ipsilateral blink (R1)
3. Ipsilateral Vm -> bilateral CNVII -> bilateral blink (R2)
A 72 year old patient is seen in clinic three months after a multilevel anterior cervical discectomy and fusion (ACDF) surgery. On examination, the patient has mild lower extremity weakness with bilateral foot drop, decreased sensation in the hands and feet, and mild hyperreflexia. What would you expect EMG findings to look like in the lower extremities?
A. Reduced amplitude in motor and sensory evoked potentials
B. Myopathic motor unit action potentials
C. Prolonged F waves and prolonged sensory evoked potentials
D. Normal motor unit action potentials with reduced activation
A. Reduced amplitude in motor and sensory evoked potentials
Explanation: The patient most likely has a diagnosis of cervical myelopathy given the physical examination, which includes upper motor neuron findings (e.g. hyperreflexia) as well as his history of ACDF. Electrodiagnostic studies should be essentially normal, including sensory evoked potentials, motor evoked potentials, and motor unit action potentials. As this is a central process, there may be reduced activation.