[A patient with myopathy due to preclinical Cushing syndrome]

A 57 year-old man with a history of diabetes mellitus was admitted to our hospital for the complaint of slowly progressive muscle weakness involving proximal limbs and head dropping. His serum CK level was within normal range, and muscle biopsy showed no inflammatory changes. To rule out myasthenia gravis, computerized tomography was done for the detection of thymoma, and detected an adrenal tumor in stead. He was not over-weighted, and his morning plasma levels of ACTH and cortisol were within normal ranges. Additional hormonal examinations revealed daily autonomous hypersecretion of cortisol. He received diagnosis of preclinical Cushing syndrome. After resection of the tumor, muscle weakness improved and his diabetes mellitus was controlled better. The muscle symptoms seem to be related with steroid myopathy. Preclinical Cushing syndrome should be included as a differential diagnosis for myopathy of unknown etiology.