Muscle breakdown and repair in polymyositis: a case study.

Muscle breakdown and repair were measured by metabolic balance techniques in a patient with polymyositis who was being treated with prednisolone and azathioprine. Changes in body muscle mass that had been estimated from nitrogen and phosphorus balances correlated with antropometric assessments of thigh muscle mass and quadriceps strength. Decline in muscle strength was associated with a net rate of muscle breakdown of 148 g/day. Recovery was associated with a net rate of muscle repair of up to 100 g/day. Early reduction in corticosteroid treatment appeared to enhance the rate of repair. Changes in the isometric contraction force of the quadriceps muscle (but not in clinical symptoms, plasma creatine kinase [CK] or erythrocyte sedimentation rate [ESR] were found to reliably indicate whether the muscle was in a state of breakdown or repair. Treatment of the individual patient may be quantitatively monitored by metabolic balance studies or, more simply, by measurement of muscle strength.