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Critical Illness Myopathy vs Polyneuropathy — FRCA Final MCQ

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HardIntensive Care MedicineCritical Illness Myopathy vs PolyneuropathyFRCA Final

A 55-year-old man on ICU has developed ICU-acquired weakness. He has been ventilated for 21 days, received corticosteroids for ARDS, and neuromuscular blocking agents for 48 hours. He has diffuse symmetrical weakness (MRC grade 3/5 in all limbs) with intact sensation. Nerve conduction studies show reduced compound muscle action potentials with preserved sensory nerve action potentials and normal conduction velocities. What is the most likely diagnosis?

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Correct answer: D — Spinal cord compression

The pattern of reduced compound muscle action potentials (CMAP) with preserved sensory nerve action potentials (SNAP) and normal conduction velocities is characteristic of critical illness myopathy (CIM), not polyneuropathy. In critical illness polyneuropathy (CIP), both motor AND sensory nerve amplitudes are reduced. Risk factors for CIM include: corticosteroid use, neuromuscular blocking agents, sepsis, and multi-organ failure. CIM generally has a better prognosis than CIP. Often both coexist (CINM – critical illness neuromyopathy). Diagnosis may require muscle biopsy or direct muscle stimulation.

Reference: ICS – 2023 – ICU-acquired weakness guidelines; RCOA – 2023 – ICM curriculum