Acute quadriplegic myopathy in a 17-month-old boy

Acute quadriplegic myopathy is a rare condition associated with the use of nondepolarizing muscle-blocking agents and corticosteroids in the course of severe systemic illness. A 17-month-old boy underwent liver transplantatio n for fulminant hepatitis. He was intubated for 24 days and treated with ve curonium bromide and high-dose methylprednisolone. The child was weaned fro m the ventilator and presented extreme weakness in the upper limbs and tota l paralysis of the lower limbs. Serum creatine kinase level was normal and electromyography showed myopathic abnormalities. Muscle biopsy Showed sever e type-1 fiber atrophy and selective loss of myosin thick filaments was see n on electron microscopy. Scattered regenerating fetal myosin-positive fibe rs were present, mu calpain was absent, while m calpain was diffusely expre ssed. Physical therapy was immediately started and the child recovered even though corticosteroids were not discontinued. The pathogenesis of acute qu adriplegic myopathy is still unknown. We suggest that it could be due to ab normal protein turnover in the muscle. Several independent factors, such as corticosteroid treatment, immobilization, or cytokines, could take part in a cascade of events that leads to an excessive yet selective degradation o f proteins involving myosin thick filaments and possibly components of sarc olemma, causing muscle inexcitability.