Critical illness myopathy associated with hyperthyroidism.

A 51-year-old woman was admitted to the intensive care unit for exacerbation of chronic obstructive pulmonary disease. She received antibiotics, neuromuscular blocking agents, and steroids. After 8 days in the intensive care unit, she was noted to be severely weak, her serum creatine kinase had risen to 1,692 U/L (normal, 20-220 U/L), and a muscle biopsy was consistent with critical illness myopathy. As a result of evaluating for resting tachycardia, the patient was found to be hyperthyroid. Her weakness rapidly improved within 1 month after treatment of her hyperthyroidism with iodine-131 and methimazole. The metabolic alterations associated with hyperthyroidism may enhance the risk of developing critical illness myopathy after the administration of antibiotics, neuromuscular blocking agents, and steroids in the intensive care unit.