Myopathy with thick filament (myosin) loss following prolonged paralysis with vecuronium during steroid treatment.

A 20-year-old female hospitalized with status asthmaticus was treated with bronchodilators, antibiotics, and high-dose corticosteroids, and was paralyzed with vecuronium for 10 days to facilitate mechanical ventilation. When this was discontinued, she was found to have a flaccid quadriplegia with areflexia and 4-fold elevation in serum creatine kinase. A muscle biopsy showed extensive loss of thick (myosin) myofilaments, sometimes in core-like distribution, with relative preservation of thin (actin) filaments and Z-discs. Muscle strength returned to normal after 2 months. The pathological lesion in this patient's muscle fibers resemble those in rats treated with high doses of corticosteroids following denervation.