Corticosteroid myopathy: a clinical and pathological study.

In six patients with Cushing's syndrome and three with steroid myopathy, the clinical, functional, biochemical and structural characteristics of myopathy are described. Proximal muscle weakness occurred in all the patients, preferentially affected the lower limbs and was accompanied by muscle wasting in all but one patient. Force measurements confirmed quadriceps weakness in every patient. Vastus lateralis muscle biopsies showed light microscopic abnormalities in two of three patients with steroid myopathy and one of five patients with Cushing's syndrome. Type II fibre atrophy was the commonest abnormality. Reduced type II mean fibre areas occurred in all the patients with steroid myopathy and were common in Cushing's syndrome patients. Type I mean fibre areas were also reduced in two of the former group and one of the latter group and two further patients in this group had areas at the lower end of the normal range. Abnormalities in electron microscopy, mitochondrial function tests and chemical content of skeletal muscle were frequent and are described and discussed. A plasma creatine kinase activity (CK) at the lower end of the normal range, a myopathic electromyogram (EMG) and a raised 24-h urinary 3-methylhistidine/creatinine ratio on a creatine free diet were other characteristic findings in both groups of patients.