Co-Occurrence of Exogenous and Endogenous Cushing's Syndromes—Dilemma in Diagnosis

Approach to patients who manifest with features of Cushing's syndrome often begin with exclusion of exposure to excessive exogenous source of glucocorticoids (GC). Most guidelines advocate no further assessment if excessive exogenous GC use is present. We present a case of a 66-year-old lady who was noted to have typical features of Cushing's syndrome. As she gave a very clear history of ingesting exogenous GC for a year, no further work up was undertaken. Despite cessation of GC for a year, she continued to have thin skin and easy bruising. Upon admission for hypertensive emergency, her clinician took note of her changes and investigated her for endogenous Cushing's syndrome. Her cortisol post overnight dexamethasone suppression test was 707 nmol/l. Post low dose dexamethasone suppression test yielded a cortisol of 1133.2 nmol/l. 24 hours urine cortisol was 432.2 nmol/l. Plasma ACTH was 1.1 pmol/l, indicating an ACTH independent Cushing's syndrome. We proceeded with Computed tomography scan (CT scan) of adrenals which revealed a right adrenal adenoma measuring 4.4 × 3.4 × 4.0 cm. Right retroperiteneoscopic adrenalectomy was done. Histopathology examination was consistent with adrenal cortical adenoma with foci of myelolipoma. Post adrenalectomy she developed hypocortisolism secondary to contralateral adrenal suppression which lasted up to the present date. Her cutaneous and musculoskeletal manifestations improved substantially. Co-occurrence of endogenous and exogenous Cushing's syndromes is uncommon but should be considered in patients whose Cushingnoid features do not resolve after cessation of exogenous GC.