Electrophysiologic studies in critical illness associated weakness: myopathy or neuropathy – a reappraisal

Objective: Unexplained weakness in critically ill patients is recognized with increasing frequency. However, it is debated whether the condition is a peripheral neuropathy or a myopathy. Diagnostic difficulties can arise from multiple sources that are not generally a factor in other neuromuscular conditions. Conventional electrodiagnostic techniques may provide only non-specific data, clinical examination is often hampered, and muscle biopsy is not a practical screening tool. Method: To improve diagnostic yield, we studied 22 consecutive patients with critical illness associated weakness with additional electrodiagnostic techniques, including direct muscle stimulation, quantitative electromyography, and motor unit number estimation. Results: The applied techniques supported an underlying myopathy in all the patients examined. The diagnosis was confirmed by muscle biopsy in 9 patients. Additional lesser features of neuropathy were concomitantly present in one patient who also underwent sural nerve biopsy. Conclusions: The study suggests that myopathy is much more common than polyneuropathy in critical illness. Suspicion of this entity should be high in this setting even without exposure to corticosteroids or non-depolarizing blocking agents.