ABEM (EDX) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

ALS diagnostic criteria

Amyotrophic lateral sclerosis is diagnosed when progressive upper and lower motor neuron signs affect at least three body regions, with no sensory loss or sphincter dysfunction.

Myasthenia gravis decrement

Repetitive nerve stimulation in myasthenia gravis typically produces a decrement greater than 10 percent in compound muscle action potential amplitude, while sensory nerve conduction remains normal.

Lambert-Eaton facilitation

Lambert-Eaton myasthenic syndrome shows low baseline compound muscle action potential amplitude and greater than 100 percent facilitation after ten seconds of maximal voluntary contraction or high-frequency stimulation.

Guillain-Barré CSF finding

Cerebrospinal fluid in Guillain-Barré syndrome often shows albuminocytologic dissociation, with elevated protein and normal cell count, supporting an inflammatory demyelinating polyradiculoneuropathy.

CIDP time course

Chronic inflammatory demyelinating polyradiculoneuropathy requires a progressive or relapsing course lasting more than eight weeks and demyelinating features in at least two nerves.

Cervical radiculopathy NCS

Cervical radiculopathy typically preserves sensory nerve action potentials because the lesion is proximal to the dorsal root ganglion, while needle EMG shows fibrillation potentials in corresponding myotomes.

Motor conduction velocity formula

Motor conduction velocity in meters per second equals the interstimulus distance in millimeters divided by the proximal-to-distal latency difference in milliseconds.

Conduction block criterion

Conduction block is defined as a proximal compound muscle action potential amplitude less than 50 percent of the distal amplitude, with little change in response duration.

Demyelinating NCS criteria

Demyelination is suggested by conduction velocity below 70 percent of the lower limit of normal, distal latency above 130 percent of the upper limit, conduction block, or temporal dispersion.

Axonal loss NCS pattern

Axonal loss reduces compound muscle action potential or sensory nerve action potential amplitude while conduction velocity remains greater than 70 percent of the lower limit of normal.

F-wave purpose

The F-wave minimal latency assesses proximal motor conduction and increases with limb length and height; absent or prolonged F-waves suggest proximal demyelination or radiculopathy.

H-reflex pathway

The H-reflex is a monosynaptic reflex recorded from the soleus after submaximal tibial nerve stimulation; prolongation suggests an S1 radiculopathy or tibial neuropathy.

Fibrillation potentials timing

Fibrillation potentials and positive sharp waves appear two to three weeks after acute nerve injury and indicate active denervation of muscle fibers.

Neurogenic MUAP features

Neurogenic motor unit action potentials have long duration, high amplitude, and often polyphasic morphology because reinnervation enlarges motor units and groups muscle fibers.

Myopathic MUAP features

Myopathic motor unit action potentials are short in duration, low in amplitude, and polyphasic, with early and rapid recruitment of many motor units.

Myotonic discharge sound

Myotonic discharges wax and wane in amplitude and frequency, producing a dive-bomber sound, and occur in myotonic dystrophy and other channelopathies.

Single-fiber EMG jitter

Single-fiber electromyography measures jitter, the variability in neuromuscular transmission time; increased jitter or blocking indicates a neuromuscular junction disorder.

Paraspinal EMG value

Needle examination of paraspinal muscles increases sensitivity for radiculopathy because these muscles are innervated by posterior primary rami and often show denervation.

Saltatory conduction

Myelinated peripheral axons conduct action potentials saltatorily between nodes of Ranvier, increasing conduction velocity compared with unmyelinated fibers of similar diameter.

Hursh equation

The Hursh equation estimates conduction velocity of myelinated mammalian nerve as approximately six meters per second per micrometer of axon diameter.

C fiber characteristics

C fibers are unmyelinated, small-diameter axons that conduct slowly at approximately 0.5 to 2 meters per second and carry pain and temperature signals.

Dorsal root ganglion location

The dorsal root ganglion lies in the intervertebral foramen; lesions proximal to it preserve sensory nerve action potentials because the peripheral sensory axon remains connected to its cell body.

Brachial plexus roots

The brachial plexus arises from roots C5 through T1 and gives rise to the median, ulnar, radial, musculocutaneous, and axillary nerves.

Common-mode rejection ratio

A differential amplifier rejects signals common to both inputs; clinical electromyography equipment should have a common-mode rejection ratio exceeding 80 decibels.

Motor NCS filter settings

Motor nerve conduction studies typically use filter settings of 2 hertz to 10 kilohertz, while sensory studies use 20 hertz to 3 kilohertz.

Supramaximal stimulus definition

A supramaximal stimulus is 10 to 20 percent above the intensity that produces no further increase in compound muscle action potential amplitude, ensuring all motor axons fire.

Ground electrode function

The ground electrode reduces 60-hertz electrical interference and should be placed between the active and reference electrodes, close to the recording site.

Patient leakage current limit

For normal condition applied parts, patient leakage current must remain below 100 microamperes to reduce risk of electrical injury during electrodiagnostic testing.

EDX report elements

An electrodiagnostic report should include the indication, technical parameters, nerve conduction and needle EMG findings, interpretation, and a specific diagnosis or differential diagnosis.

Pacemaker stimulation caution

Electrical stimulation in patients with pacemakers or implanted defibrillators requires caution because current can travel through the chest and interfere with device sensing or pacing.

Needle EMG bleeding risk

Severe thrombocytopenia or coagulopathy increases bleeding risk from needle electromyography; the risk of hematoma must be weighed against diagnostic benefit.

CPT unbundling violation

Billing each component of a nerve conduction study separately when a single code applies is unbundling, a compliance violation that can result in fraud penalties.