A 69-year-old man was admitted because of subacute development of lower limb weakness from one month ago. He showed central obesity, gynecomastia, dorsal fat pad ("buffalo hump"), and proximal muscle weakness in the lower extremities (manual muscle test 4). Needle EMG, muscle MRI and labolatry screening including CPK were negative for neuromuscular diseases, except for the hypogenitalism accidentally detected in MRI. Although blood corticol was in normal range, the levels of serum ACTH and 24-hour urinary free cortisol excretion were high, and the dexamethasone suppression tests were positive. Brain MRI showed a small pituitary mass with gadolinium enhancement, and ACTH measurement from petrosal sinus sampling after CRH stimulation lead to the diagnosis of definite Cushing disease. Moreover, he also showed low testosterone and elevated LH and FSH. Chromosome banding revealed 47 XXY in 22 in 30 cells, leading to the diagnosis of mosaic Klinefelter syndrome. The supplementation with testosterone was partially effective for his weakness. The surgical resection of pituitary microadenoma resulted in the full recovery. Either Klinefelter syndrome or mild Cushing disease alone was insufficient as a cause of the muscle weakness in this patient. It is plausible that the mild elevation of cortisol accompanied by the lack of tesstelone may underlie the weakness, probably linked to impaired balance between muscle anabolism and catabolism.
Keywords: Cushing disease; Klinefelter syndrome; muscle weakness; steroid myopathy; testosterone.