Neuromuscular Disorders & Diagnostic Criteria Flashcards

On needle EMG, which MUAP characteristic most strongly suggests a myopathic process?

Answer: Early recruitment of short-duration, low-amplitude, polyphasic MUAPs

Myopathic MUAPs are short in duration and low in amplitude due to loss of muscle fibers per motor unit, and early recruitment occurs because more units fire to compensate for reduced force per unit.

In critical illness polyneuropathy (CIP), which electrodiagnostic pattern is expected?

Answer: Axonal sensorimotor neuropathy with low CMAP and SNAP amplitudes and active denervation

CIP is an axonal sensorimotor polyneuropathy occurring in critically ill patients, characterized by reduced CMAP and SNAP amplitudes with fibrillations on needle EMG, without significant conduction velocity slowing.

A patient with diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) would most likely show which finding on needle EMG of the affected limb?

Answer: Active denervation in multiple lumbar myotomes including paraspinal muscles

Diabetic amyotrophy (Bruns-Garland syndrome) affects lumbosacral plexus and roots, causing active denervation across multiple myotomes including paraspinal muscles, confirming the proximal and radicular involvement.

Which electrodiagnostic feature differentiates multifocal motor neuropathy (MMN) from ALS?

Answer: MMN shows conduction block in motor nerves without sensory involvement; ALS does not

MMN is defined by persistent, multifocal motor conduction block with preserved sensory conduction, while ALS shows pure lower motor neuron and upper motor neuron signs without conduction block.

In hereditary neuropathy with liability to pressure palsies (HNPP), NCS most commonly reveals:

Answer: Focal conduction slowing or conduction block at typical entrapment sites with mild diffuse slowing

HNPP (PMP22 deletion) causes disproportionate focal slowing or block at entrapment sites (carpal tunnel, fibular head) superimposed on mild diffuse sensorimotor demyelinating changes.

Which pattern on NCS best supports a diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) rather than CMT1A?

Answer: Asymmetric, multifocal slowing with conduction block and temporal dispersion

CIDP characteristically shows asymmetric or multifocal demyelination with conduction block and temporal dispersion, while CMT1A shows uniform, symmetric slowing without block.

In inclusion body myositis (IBM), which combination of needle EMG findings is most characteristic?

Answer: Mixed pattern with both myopathic and neuropathic MUAP features plus active denervation

IBM uniquely shows a mixed pattern on EMG with both short-duration myopathic MUAPs and long-duration neuropathic MUAPs, along with fibrillation potentials, reflecting the combined inflammatory and degenerative pathology.