Subclinical Cushing’s Syndrome in an ACTH-secreting Pituitary Macroadenoma

Introduction:
Subclinical Cushing’s syndrome (SCS) is characterized by subtle cortisol hypersecretion, which does not result in the typical signs and symptoms of Cushing’s syndrome (CS). While many of the signs and symptoms of CS are common in the general population, there are some that are discriminatory and specific for CS: supraclavicular fat pads, proximal muscle weakness, facial plethora, and violaceous striae. SCS manifests mostly as obesity, type 2 diabetes, and hypertension. Diagnosing SCS is challenging; however, the best screening test to uncover the subtle hypercortisolism is the dexamethasone suppression test (DST).

Case Description:
We report a case of SCS in a 62 years old Caucasian postmenopausal patient with a medical history of total thyroidectomy for Graves’ disease, post-surgical hypothyroidism, 7.4cm right pheochromocytoma status post partial right adrenalectomy, incidentally discovered pituitary macroadenoma (during imaging to look for subarachnoid hemorrhage), untreated type 2 diabetes mellitus (A1c 6.6% and stable for 1 year before treatment), hypertension, atrial fibrillation, cerebrovascular accident, and worsening migraines. Patient’s physical exam was mostly unremarkable; she had central obesity and bilateral lower extremity swelling. Pituitary work-up showed evidence of secondary hypogonadism and secondary hypothyroidism with elevated adrenocorticotropic hormone (ACTH) of 130 (AM range: 7.2-63) and cortisol of 12.6, at 11:52AM.  Further work-up for hypercortisolism revealed non-suppressed cortisol (5.83mcg/dL) on the low dose DST and 49% suppression of cortisol and ACTH on the high dose DST. 24hour urinary cortisol was normal. Patient did not perform the midnight salivary cortisol. Patient subsequently underwent trans-sphenoidal resection of the pituitary macroadenoma. Pathology analysis of the pituitary mass showed weak to moderate immunoreactivity for ACTH.

Discussion:
Our patient had abnormal DST but normal 24hour urine cortisol. We may have missed her SCS if we screened her only with a 24hour urine cortisol. This confirms the fact that dexamethasone suppression test should be the first test in the evaluation of subclinical Cushing’s syndrome.