Monograph: Electrophysiology of Neuromuscular Disorders in Critical Illness-Article

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This AANEM monograph reviews how electrodiagnostic (EDx) testing helps evaluate neuromuscular weakness in intensive care unit (ICU) patients, where clinical examination is often limited. The dominant ICU-acquired causes are critical illness myopathy (CIM), critical illness polyneuropathy (CIP), and their overlap (critical illness neuromyopathy, CINM). The paper outlines common indications for ICU EDx (diffuse weakness and ventilatory failure), practical challenges (electrical artifact, cool limbs, edema, limited access due to lines/wounds, and safety concerns such as avoiding studies in patients with external pacemakers), and a pragmatic approach to nerve conduction studies (NCS) and needle EMG in the ICU.<br /><br />Epidemiologic data show ICU-acquired weakness is frequent in severe illness (often 25–40% clinically, higher in select cohorts), with CIM often more common than CIP in comprehensive EDx studies. Major risk factors include sepsis/SIRS (especially for CIP), illness severity, hyperglycemia, and possibly neuromuscular blocking agents, aminoglycosides, and corticosteroids (stronger historical association for CIM, now more nuanced).<br /><br />The monograph emphasizes distinguishing EDx patterns. CIM typically shows markedly low motor CMAP amplitudes with relatively preserved sensory SNAPs, normal conduction velocities, frequent fibrillation potentials, and myopathic motor unit potentials; a key supportive feature is prolonged CMAP duration reflecting sarcolemmal inexcitability. CIP usually presents as a generalized axonal sensorimotor polyneuropathy with low CMAP and SNAP amplitudes but normal velocities and normal CMAP duration, with denervation and reduced recruitment on needle exam. Because ICU sensory studies are confounded by edema and artifact, interpretation must be cautious.<br /><br />For research or difficult cases, direct muscle stimulation and excitability measures can better separate CIM from CIP; muscle biopsy can confirm CIM (notably myosin/thick filament loss). Prevention/management remains largely supportive (early mobilization, careful medication and glucose management), and outcomes appear generally better for CIM than CIP.

Keywords

electrodiagnostic testing

ICU-acquired weakness

critical illness myopathy

critical illness polyneuropathy

critical illness neuromyopathy

nerve conduction studies

ncs

needle electromyography

CMAP duration prolongation

axonal sensorimotor polyneuropathy

direct muscle stimulation