Case 11-1997: Critical-Illness Myopathy

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Abstract
In discussing Case 11-1997 (April 10 issue),1 Sandrock directs attention to a “critical-illness myopathy associated with myosin deficiency.” This diagnosis is clearly based on, in addition to pathological muscle findings, the electrophysiologic studies performed on the 34th and 78th hospital days. However, the reported results of nerve-conduction studies, which included F-wave recordings, point to contemporaneous peripheral-nerve involvement. At the first examination in particular, median, ulnar, and tibial F waves were absent; at the second examination, the median F wave was still absent, the compound muscle responses were further prolonged, and the recovery in the amplitude of the compound muscles was slight and actually absent in one nerve. Indeed, the involvement of the peripheral nervous system is suggested mainly by the absence of sensory-nerve (ulnar and sural) action potentials and by the significant reduction in amplitude (from 12.4 to 5.4 μV in the median nerve) recorded in the second study. No clinical data in keeping with these findings are reported. Our opinion is that the patient had a critical-illness neuromyopathy, even if there was prominent muscle damage. The coexistence of a mild neuropathic process has been previously described in such patients 2-5 and probably results from a variety of causes. As stated,1 muscle denervation could facilitate a particularly severe form of corticosteroid-induced myopathy.