Abnormal glucose tolerance in a patient with pheochromocytoma and ACTH-independent subclinical Cushing’s syndrome involving the same adrenal gland

Coexistence of adrenocorticotropin hormone (ACTH)-independent subclinical Cushing’s syndrome (SCS) with pheochromocytoma involving the same adrenal tumor is rare. Moreover, no previous reports have compared pre- and postoperative insulin sensitivities in these cases. A 74-year-old woman was admitted to our hospital with hyperhidrosis, dry mouth, and weight loss. Pheochromocytoma was suspected based on elevated circulating catecholamines, and was confirmed by scintigraphy and histopathological analysis. Laboratory data, low ACTH, and lack of a diurnal cortisol rhythm indicated coexisting Cushing’s syndrome (CS). The atypical symptoms of CS and lack of cortisol suppression after 1 and 8 mg dexamethasone suppression tests confirmed the diagnosis of SCS. Histopathological analysis demonstrated autonomous cortisol production caused by paracrine stimulation from the pheochromocytoma. Her fasting plasma glucose level on admission was 372 mg/dL and her hemoglobin (Hb) A1c was 11.0%. HbA1c decreased to 5.2% postoperatively, with improved insulin secretion indicated by homeostasis model assessment β (18.1 to 45) and urinary C-peptide (26.5 to 48.5 mg/day). Herein we report a rare case of pheochromocytoma and SCS involving the same adrenal tumor, with the first documented levels of glucose tolerance before and after surgery. Coexisting SCS should thus be considered in patients with pheochromocytoma presenting with severely uncontrolled diabetes mellitus.