ABPN Neuromuscular Medicine key terms

A clinical finding caused by damage to the anterior horn cell, motor root, or peripheral nerve, producing weakness, muscle atrophy, fasciculations, and reduced deep tendon reflexes in the affected distribution.

A clinical finding from damage to corticospinal pathways, producing spasticity, hyperreflexia, extensor plantar responses, and loss of fine dexterity, with minimal atrophy and no fasciculations.

A spontaneous, brief, visible twitch of a group of muscle fibers within one motor unit, reflecting irritability of motor axons or anterior horn cells; widespread fasciculations with weakness suggest motor neuron disease.

A spontaneous, single-fiber electromyographic discharge from a denervated muscle fiber, appearing as a brief regular spike on needle EMG; it indicates active denervation rather than a visible clinical twitch.

A spontaneous needle EMG waveform with an initial positive deflection followed by a slow negative return, generated by an irritable denervated muscle fiber and signaling active denervation or muscle membrane instability.

A test in which a needle electrode records electrical activity of muscle at rest and during voluntary contraction, used to localize denervation, myopathy, or neuromuscular junction dysfunction.

A test that applies electrical stimulation to nerves and records the resulting compound responses, measuring conduction velocity, distal latency, and amplitude to distinguish axonal loss from demyelination.

The summed electrical response recorded from a muscle after supramaximal stimulation of its motor nerve; reduced amplitude suggests axonal loss, while prolonged latency or slowed conduction suggests demyelination.

The summed response recorded from a sensory nerve after electrical stimulation; it is reduced or absent in sensory axonal loss or ganglionopathy and may be preserved in preganglionic lesions.

A fall in CMAP amplitude on proximal versus distal stimulation without abnormal temporal dispersion, indicating focal demyelination along a nerve segment; a hallmark of acquired demyelinating neuropathies such as CIDP.

Prolonged, widened, and reduced CMAP waveforms caused by unequal conduction slowing among fibers in a demyelinated nerve segment; it reflects acquired demyelination and can mimic conduction block.

The electrical signal recorded from a single motor unit during voluntary contraction; its duration, amplitude, and recruitment pattern help distinguish neurogenic (large, long) from myopathic (small, short) changes.

The orderly activation of additional motor units as voluntary effort increases; reduced recruitment with rapid firing suggests neurogenic loss, while early recruitment of many small units suggests myopathy.

A needle EMG finding of brief-duration, low-amplitude, polyphasic motor unit potentials with early recruitment, typical of muscle fiber loss or disorganization in myopathies.

A test that delivers repeated supramaximal stimuli to a motor nerve and measures CMAP decrement; a decrement greater than about 10% supports a postsynaptic neuromuscular junction disorder such as myasthenia gravis.

A highly sensitive needle EMG technique measuring jitter and blocking between two muscle fibers of the same motor unit; increased jitter indicates neuromuscular junction transmission instability.

The variability in latency between two muscle fibers of the same motor unit recorded with single-fiber EMG; increased jitter reflects unstable neuromuscular junction transmission and is the most sensitive marker of myasthenia gravis.

A progressive neurodegenerative disorder affecting upper and lower motor neurons, producing painless weakness, atrophy, fasciculations, spasticity, and often bulbar and respiratory involvement, with no sensory loss.

A diagnostic framework for ALS that combines upper and lower motor neuron findings across body regions and requires exclusion of mimics; levels range from possible to definite ALS.

An acute immune-mediated polyradiculoneuropathy presenting with progressive symmetric weakness, areflexia, and often antecedent infection; respiratory and autonomic monitoring is essential because of possible rapid deterioration.

The most common subtype of Guillain-Barré syndrome, characterized by demyelinating nerve conduction changes, ascending weakness, and areflexia, often following a gastrointestinal or respiratory infection.

An acquired immune-mediated demyelinating neuropathy with progressive or relapsing weakness lasting more than eight weeks, supported by nerve conduction studies and responsive to immunomodulatory therapy.

Elevated cerebrospinal fluid protein without a proportional increase in white blood cells, classically seen in Guillain-Barré syndrome and other inflammatory polyradiculoneuropathies.

A neuropathy pattern on nerve conduction studies with slowed conduction velocity, prolonged distal latencies, or conduction block, reflecting myelin damage rather than primary axonal loss.

An autoimmune disorder of the neuromuscular junction, usually from acetylcholine receptor antibodies, causing fatigable ptosis, diplopia, bulbar weakness, and proximal weakness that worsens with activity.

A presynaptic neuromuscular junction disorder caused by antibodies to voltage-gated calcium channels, producing proximal weakness that improves with activity, hyporeflexia, and frequent association with small-cell lung cancer.

A group of immune-mediated muscle diseases, including dermatomyositis, polymyositis, and immune-mediated necrotizing myopathy, causing proximal weakness, elevated creatine kinase, and myopathic EMG findings.

A muscle enzyme measured in serum; marked elevation suggests active muscle injury such as inflammatory myopathy or dystrophy, while normal levels do not exclude neurogenic weakness.

Histologic examination of muscle tissue used to identify inflammation, dystrophic changes, storage material, or mitochondrial abnormalities when clinical, laboratory, and electrodiagnostic findings are inconclusive.

A group of inherited progressive muscle disorders caused by mutations affecting muscle structural proteins, producing weakness, elevated creatine kinase, and characteristic biopsy or genetic findings.

A group of inherited peripheral neuropathies, most commonly demyelinating (CMT1) or axonal (CMT2), causing distal weakness, atrophy, sensory loss, pes cavus, and often a family history.

An autosomal dominant neuropathy, usually from PMP22 deletion, causing recurrent painless focal mononeuropathies at compression sites, with nerve conduction showing widespread mild slowing.

Involvement of multiple individual peripheral nerves in an asymmetric, stepwise pattern, often from vasculitis, diabetes, or infection; it suggests ischemic or inflammatory nerve damage.

Peripheral nerve damage from inflammation and occlusion of nerve blood vessels, producing painful, asymmetric mononeuropathy multiplex or overlapping polyneuropathy, often with systemic vasculitis.

A neuropathy pattern with reduced CMAP or SNAP amplitudes and relatively preserved conduction velocities, reflecting loss of axons rather than myelin; common causes include toxins, diabetes, and heredity.

The cluster of sensory neuron cell bodies outside the spinal cord; lesions here (ganglionopathy) cause sensory loss with reduced SNAPs, while preganglionic root lesions may spare SNAPs.

Histologic examination of a sensory nerve, usually sural, used to diagnose vasculitis, amyloidosis, or other infiltrative neuropathies when less invasive testing is nondiagnostic.

Placement of a needle into the spinal subarachnoid space to collect cerebrospinal fluid for cell count, protein, glucose, and specific testing, useful in suspected inflammatory or infectious neuropathies.