A 54 year old man presented to hospital with a 10 day history of progressive, profound muscle weakness, to the extent that he was unable to walk. At admission, he described a resolving flu-like illness with dark red urine. There was no rash, arthritis or oral ulcers. Past history was remarkable for coronary artery bypass grafting, urolithiasis, and benign prostatic hypertrophy. He had hypercholesterolemia for which he had taken lovastatin 120mg and niacin 3g daily for the past twelve months. He was otherwise in good health.
Examination revealed profound proximal muscle weakness with muscle tenderness. No rashes or Gottron's papules were present. Serum creatine kinase level was 121 000 U/l. Myoglobinuria was confirmed.
He was admitted with a clinical diagnosis of acute polymyositis and corticosteroids were begun. An electromyogram demonstrated fibrillation potentials and short, polyphasic motor unit potentials in the left deltoid and left biceps. A right quadriceps muscle biopsy was performed.