Table 1.

Features of Neuromuscular Abnormalities of Critical Illness^a

	Critical Illness Polyneuropathy	Critical Illness Myopathy	Disuse Atrophy
Setting	Sepsis, SIRS, MODS	Most common with NMBAs, steroids, asthma, organ transplant	Prolonged bed rest/immobility Prolonged sedation
Clinical features	Generalized or distal muscle weakness Cranial nerves usually spared Distal sensory deficit Preserved or depressed DTRs	Generalized or predominantly proximal muscle weakness No sensory impairment Preserved or depressed DTRs Elevated CK levels: 10- to 100-fold	Muscle wasting with flaccid weakness Normal or reduced strength with marked diminished endurance No sensory deficits Preserved DTRs
Nerve conduction studies	CMAP decreased to <80% of LLN in >2 nerves SNAP decreased to <80% of LLN in > 2 nerves Normal conduction velocity	CMAP decreased to <80% of LLN in > 2 nerves SNAPs are >80% of LLN in >2 nerves NCVs normal or near-normal without conduction block	Normal NCS, or Modest decreased CMAP with preserved SNAP
Needle EMG	Abnormal spontaneous activity Large polyphasic MUAPs Reduced recruitment/interference pattern	Variable spontaneous activity Small polyphasic MUAPs in >2 muscle groups, Low-amplitude, full interference pattern	Abnormal/absence of spontaneous activity Polyphasic MUAP
Direct muscle stimulation	Reduced ne-CMAP Normal dm-CMAP ne-CMAP to dm-CMAP ratio <0.532	Reduced ne-CMAP and dm-CMAP ne-CMAP: dm-CMAP ratio > 0.5 in >2 muscle groups
Biopsy	Axonal degeneration of motor and sensory nerve fibers	Thick filament (myosin) loss Necrotizing myopathy Inflammatory infiltrate may be present	Shift from slow twitch (type I) to fast twitch (type II) muscle fibers Decreased muscle fiber size Little or no inflammatory infiltrates

^a Modified from Stevens R¹¹ and Fan E.²⁷

Abbreviations: CK, serum creatine kinases; CMAP, compound muscle action potential; dm-CMAP, direct muscle stimulated muscle action potential; DTRs, deep tendon reflexes; LLN, lower limit of normal; MODS, multiple organ dysfunction; MUAP, motor-unit action potential; ne-CMAP, nerve stimulated compound muscle action potential; NMBAs, neuromuscular blocking agents; NCVs, nerve conduction velocities; SIRS, systemic inflammatory response syndrome; SNAP, sensory nerve action potential.