Effect of treatment of Cushing's syndrome on skeletal muscle structure and function.

The time course of recovery in the myopathy of Cushing's syndrome was studied before and after removal of a pituitary adenoma at hypophysectomy in three patients and an adrenal adenoma in another. Serial measurements were performed of quadriceps force, total muscle mass/body weight, individual fibre size on needle biopsies of the lateral muscle mass of the thigh and skeletal muscle cross-sectional area (CSA) and force/unit CSA on computed (CT) scans of thighs and calves. All patients were weak, and recovery was slow but substantial except in one patient who had persistent Cushing's syndrome. An accompanying increase in overall and type II mean fibre area (MFA) occurred after surgery in the patients with a pituitary adenoma, as did an increase in skeletal muscle CSA and force/unit CSA in both patients having CT scans. The only patient with pronounced muscle wasting showed severe type II fibre atrophy with a reduced total muscle mass/body weight, but muscle morphology and total muscle mass were normal in the other patients. Only in this patient was a significant increase in total muscle mass/body weight noted after surgery. These findings suggest that the increase in muscle mass which may follow hypophysectomy in Cushing's syndrome is due to an increase in individual cell size.