Potent Potables
Which of the following is true regarding sympathetic skin response studies?
a.) The recording electrode can be placed at any location on the upper or lower extremities
b.) Stimulations need to be carried out at regular intervals
c.) SSR is a means of evaluating myelinated sympathetic nerve fibers of the peripheral nervous system
d.) Improper stimulation patterns often lead to nerve habituation
d.
In general, what are the expected findings on nerve conductions for a demyelinating peripheral neuropathy?
Prolonged distal latency, slowed conduction velocity, increased temporal dispersion, conduction block
In general, what are the expected findings on NCS in a primary axonal peripheral neuropathy?
Reduced CMAP and SNAP amplitude, normal latency and CV
Which HMSN type typically presents as an axonal, motor > sensory neuropathy?
a. HMSN I
b. HMSN II
c. HMSN III
d. HMSN IV
b is correct. The other options present as a uniform demyelinating sensorimotor neuropathy
Which of the following typically presents as a segmental, demyelinating neuropathy?
a. Diabetes mellitus
b. Porphyria
c. AIDP
d. Friedreich's ataxia
c is correct.
DM is demyelinating/axonal, sensorimotor
Porphyria is axonal, motor > sensory
Friedreich's ataxia is sensory axonal
What type of peripheral neuropathy is typically caused by EtOH? (dymyelinating/axonal, sensory/motor)
Axonal, sensorimotor
Which Edx finding would not be expected in HMSN Type I?
a. Abnormal SNAP
b. Decreased conduction velocity
c. Temporal dispersion
d. Normal EMG (no fib's/PSW's)
c. This is a uniform demyelinating process. Temporal dispersion indicates range between the fastest and slowest fibers. In this process, the fibers are equally demyelinated, and firing at relatively similar velocities.
What is the most common worldwide neuropathy?
Leprosy (segmental demyelination, motor > sensory)
A lesion producing scapular winging upon elevation of the outstretched arm in the forward position would most likely be in the:
A. Long thoracic nerve.
B. Accessory nerve.
C. Suprascapular nerve.
D. Axillary nerve.
E. Thoracodorsal nerve.
A. Forward elevation of the outstretched arm against gravity requires forward and lateral rotation of the scapula on the chest wall. This scapular rotation occurs by means of a 3-part force coupled on the scapula. The serratus anterior (supplied by the long thoracic nerve) pulls the inferior angle of the scapula forward against the posterior lateral chest wall, the upper trapezius (supplied by the accessory nerve) pulls the lateral scapula upward, and the lower trapezius (supplied by the accessory nerve) pulls the medial scapula downward and stabilizes it medially. Therefore, a long thoracic nerve lesion (A) causes scapular winging with forward elevation of the outstretched arm. An accessory nerve lesion (B) causes impaired scapular rotation on the chest wall with lateral elevation of the outstretched arm. Suprascapular nerve palsy (C) may impair elevation of the arm due to weakness of the supraspi
Common mode rejection involves:
A. Suppression of signals recorded equally by both active and reference electrodes.
B. Display of signals recorded equally by both active and reference electrodes.
C. Normalizing the impedance between the active and reference electrodes.
D. The inversion of the signal recorded by the active electrode.
E. Changing waveform configuration by altering filter parameters.
A. An important property of differential amplifiers is their ability to discriminate against artifact potentials that appear equally at both amplifier input terminals (common mode signals) and to amplify the desired potentials that appear as different signals at the 2 input terminals. A technical measure of the ability of a differential amplifier to discriminate against common mode signals is called its common mode rejection ratio. Ideally, any voltage identically present at both electrodes will not be amplified, since only the difference between the 2 points is to be multiplied.
A patient is known to have complete transection of the median nerve at the wrist. Despite this he has functional opposition and abduction of the thumb. Needle EMG of the abductor pollicis brevis and opponens pollicis reveals fibrillation potentials with some MAUPs of varying complexity. Which of the following anomalous innervations would most likely account for these findings?
A. The anterior interosseous nerve to the ulnar motor nerve.
B. The ulnar motor nerve to the median motor nerve in the forearm.
C. The deep ulnar nerve with the recurrent branch of the median nerve.
D. The Martin–Gruber anastomosis.
E. The accessory deep peroneal nerve.
C. The Riche-Cannieu anastamosis (communication between the recurrent branch of the median nerve and the deep ulnar nerve in the hand) could account for the volitional motor units seen in the abductor pollicis brevis (APB) and opponens pollicis (OP) and preserved clinical function in this case. A Martin-Gruber anastomosis (which most commonly involves communication between the anterior interosseous nerve and ulnar motor nerve in the forearm) alone would not account for the preserved function of these the OP and APB. An accessory deep peroneal nerve would arise from the superficial peroneal nerve in the leg and supply the extensor digitorum brevis muscle.
The earliest common electrophysiologic abnormality encountered in an acute inflammatory demyelinating polyneuropathy is:
A. Delayed or absent F waves and H reflexes.
B. Small motor response amplitude.
C. Slowed sensory conduction velocity.
D. Delayed motor terminal latency.
E. Conduction block and temporal dispersion.
A. The earliest and most common electrophysiologic changes in acute inflammatory demyelinating polyneuropathy is delayed, absent, or in persistent F-wave and H-reflex responses, usually encountered within a few days and reflecting proximal demyelination. Delayed motor terminal latency, conduction block, and temporal dispersion occur later and are present in about 50% of patients by 2 weeks and in 85% by 3 weeks. However, a small number of patients have inexcitable nerves early on, either from axonal degeneration or from presumed distal demyelination.
Hereditary neuropathy with liability to pressure palsy is characterized by which of the following?
A. Autosomal recessive inheritance.
B. X-linked inheritance.
C. Painful neuropathy.
D. Tomaculae.
E. Primarily axonal neuropathy.
D. Hereditary neuropathy with liability to pressure palsy (HNPP) is characterized by tomaculae on nerve biopsy. Tomaculae are focal globular thickenings of myelin sheath, resembling sausages. HNPP is autosomal dominant with painless weakness and numbness.
Lead neuropathy often presents with what type of mononeuropathy?
a. AIN
b. Long Thoracic Nerve
c. Radial Nerve
d. Axillary Nerve
c. Radial Nerve (wrist drop). Other symptoms can include progressive UE weakness, encephalopathy, blue lines in gums, blindness. Anormal Radial CMAP and EMG
Axonotmesis is characterized by:
A. Loss of axon but retained epineurium continuity.
B. Loss of axon and loss of epineurium continuity.
C. Persistent segmental conduction block.
D. Axonal preservation but Schwann cell injury.
E. Incompatibility with spontaneous recovery.
A. Axonotmesis is characterized by axonal injury leading to Wallerian degeneration but preserved connective tissue layers, including the surrounding endoneurium, perineurium, and epineurium. Loss of all connective tissue layers is indicative of the most severe grade of injury (neurotmesis) and is incompatible with spontaneous recovery. Recovery is possible if the connective tissue sheath persists despite axonal degeneration. Neurapraxia is characterized by segmental conduction block but minimal inherent axonal pathology, other than intraneural edema and increased pressure in more severe grades.
Varying or unstable motor unit potentials occur in which of the following?
A. Acute, complete nerve transection.
B. Lambert-Eaton myasthenic syndrome.
C. Neurapraxia.
D. Steroid myopathy.
E. Stroke.
B. Motor unit potentials normally have the same amplitude, duration, and configuration with each firing. Fluctuation of any of these variables during repeated discharges of an MUP is abnormal and produces varying or unstable MUP. Varying MUPS are caused by blocking of the discharge of action potentials of one or a few of the individual muscle fibers comprising the motor unit. In LEMS, the action potential does not reach threshold in one or few of the muscle fibers comprising the motor unit.
A patient with progressive sensorimotor neuropathy demonstrates severely and disproportionately prolonged distal motor latencies and diffusely absent sensory nerve action potentials. No site of focal motor conduction block is identified. Which antibody is most likely to be present in this patient?
A. Acetylcholine receptor antibodies.
B. Myelin-associated glycoprotein antibodies.
C. GM1 ganglioside antibodies.
D. Voltage-gated potassium channel antibodies.
E. Voltage-gated calcium channel antibodies.
B. Antibodies against myelin-associated glycoprotein (anti-MAG) are associated with often severe sensorimotor neuropathy. Most cases with high anti-MAG titers have an underlying paraproteinemia, usually of the immunoglobulin M type. Patients are generally over age 50. Tremor is also common. Electrodiagnostic studies characteristically demonstrate severe distal motor latency prolongation and a lesser degree of conduction velocity slowing and temporal dispersion, but generally no conduction block. The disparity between distal and more proximal slowing can be highlighted with measures that compare distal to more proximal conduction times, including the terminal latency index and residual latency. GM1 ganglioside antibodies are seen in 30-40% of patients with multifocal motor neuropathy. Conduction block is a characteristic, but not universally present, feature. In addition, sensory responses show minor or no abnormalities but are not absent. Voltage-gated potassium channel antibodies are associated with Isaacs’ syndrome, cramp fasciculation syndrome and other hyperexcitability syndromes, and limbic encephalitis. Acetylcholine receptor (AChR) antibodies are seen in a majority of myasthenia gravis patients; antibodies to nonneuromuscular junction AChRs are associated with other disorders such as epilepsy and autonomic neuropathy. Voltage-gated calcium channel antibodies are associated with the Lambert–Eaton myasthenic syndrome.
A previously healthy 54-year-old male developed severe burning pain in his fingertips and numbness in his feet with profound fatigue and mild cardiomyopathy over the last 4 months. He suffers with impotence for 1 year and now has recurrent diarrhea. There is no history of diabetes, normal fasting glucose, and no known toxic exposure. Nerve conduction testing shows absent sensory potentials in the lower extremities and severe bilateral carpal tunnel syndrome. Which one of the following tests will be most likely abnormal and diagnostic?
A. Serum levels of vitamin B12 and methylmalonic acid.
B. Glucose tolerance test.
C. Rectal biopsy.
D. Abdomen and chest computed tomography scan.
E. Cerebral spinal fluid Lyme polymerase chain reaction.
C. Nonhereditary amyloid neuropathy is predominantly sensory with prominent early loss of small fibers, followed by progressive weakness and large-fiber involvement. Dysautonomia is often severe and disabling, as is the pain associated with small fiber damage. Diagnosis depends on the histological demonstration of amyloid either in the rectal or nerve biopsy. Rectal biopsy is positive in 70% of cases, but it must include the submucosa because that tissue is involved more frequently than mucosa.
Which axonal sensorimotor neuropathy characteristically exhibits + birefringement with Congo red staining on biopsy?
a. EtOH
b. Amyloidosis
c. Sarcoidosis
d. Uremia
Answer b. Biopsy for Etoh shows Wallerian degeneration. Biopsy in Sarcoid shows sarcoid tubercles. Biopsy in uremia shows demyelinating and axonal type damage.
At what level of entrapment of the suprascapular nerve can isolated atrophy of the infraspinatus muscle be caused?
A. Suprascapular notch.
B. Spinoglenoid notch.
C. Quadrangular space.
D. Interscalene triangle.
E. Erb’s point.
B. After branching off from the upper trunk of the brachial plexus, the suprascapular nerve traverses the suprascapular notch to enter the supraspinous fossa, innervating the supraspinatus muscle. It then passes through the spinoglenoid notch to enter the infraspinous fossa and innervate the infraspinatus muscle. Entrapment at this level would result in isolated atrophy and weakness of the infraspinatus.
What is Roussy-Levy Syndrome?
CMT plus essential tremor
Which of the following patterns of EDX abnormalities would be most likely in a patient with diffuse polyneuropathy caused by nutrient deficiency after bariatric surgery for obesity?
A. Sensory motor NCS abnormalities, decreased NCS amplitudes, normal NCS latencies and conduction velocities.
B. Multiple sites of conduction block occurring at locations of common compression neuropathies.
C. Prolongs NCS latencies, normal NCS amplitudes, decreased conduction velocities, and prolonged F-waves.
D. Normal sensory NCS findings, decreased compound muscle action potentials amplitudes, and diffuse abnormal spontaneous activity on needle EMG examination.
E. Multiple sites of conduction block not occurring in locations of common compression neuropathies.
A. Following bariatric surgery for obesity, multiple neurologic complications may occur. A diffuse polyneuropathy caused by nutrient deficiency is among the most common causes of neurologic impairment after bariatric surgery. This may be due to isolated thiamine deficiency (which may occur with or without Wernicke's encephalopathy) or multiple vitamin deficiencies. Nutritional supplementation following bariatric surgery is important to prevent neurologic complications. The neuropathy is typically axonal in nature (with decreased nerve conduction study amplitudes and normal latencies and conduction velocities) with sensory greater than motor involvement. The other answer choices describe demyelinating neuropathies or motor-predominant neuropathies.
Which of the following is true regarding a standard concentric needle electrode?
A. It records motor unit potentials of higher amplitude than those seen with a monopolar needle electrode.
B. It is usually used in conjunction with a surface reference electrode.
C. It records motor unit potentials from several muscle fibers near the tip of the recording electrode.
D. It has a smaller recording surface than a single-fiber electrode.
E. It has the same size recording surface as a macro-EMG electrode.
C. The standard concentric needle electrode records activity within 1-2.5 mm of the tip of the electrode. Its recording surface of 150 um is larger than that of a single fiber electrode (25 um) but smaller than a macro-EMG electrode (15 mm). Monopolar needle electrodes, which use a surface reference electrode, record a larger area and will have a slightly higher amplitude and longer duration.
Multiple motor conduction blocks, not at typical sites of compression, are a hallmark feature of which disorder?
A. Multifocal motor neuropathy.
B. Hereditary motor and sensory neuropathy type I.
C. Mononeuropathy Multiplex.
D. Hereditary neuropathy with liability to pressure palsies.
E. Diabetic polyneuropathy.
Multiple conduction blocks are a characteristic feature of multifocal motor neuropathy. Some patients have associated GM1 ganglioside antibodies. A diligent electrophysiological evaluation is critical because this condition is treatable and may mimic motor neuron disease in some cases. Motor conduction blocks typically involve unusual sites such as median nerve in the forearm or elements of the brachial plexus rather that common sites of nerve compression or entrapment. Most patients have selective involvement of motor fibers with normal sensory conduction through the sites of motor conduction block but some have minor sensory changes. The focal conduction blocks can also be very proximal or very distal in the nerve territory and may require nerve simulation at uncommon sites. Conduction block may be observed in patients with hereditary neuropathy with liability to pressure palsies, linked to deletions in the PMP22 gene, but most commonly occur at typical sites of nerve compression. Other hereditary axonal and demyelinating neuropathies usually do not demonstrate conduction block but instead have uniform slowing (type 1) or axonal loss (type 2)
F-wave persistence is lowest for which of the following nerves?
A. The peroneal nerve.
B. The tibial nerve.
C. The ulnar nerve.
D. The median nerve.
E. The radial nerve.
A. Peroneal
F-wave persistence is the percentage of stimuli that produce F waves. The peroneal nerve has the lowest persistence at around 5%. The tibial, ulnar, median, and radial nerves have a much higher persistence, around 40%.