Adrenal incidentalomas can present with subclinical Cushing’s Syndrome (SCS), which is defined as elevated cortisol levels without overt clinical signs or symptoms. Inaccuracies in ACTH levels due to issues with the assay and non-classic presentation of Cushing’s Syndrome (CS) can delay appropriate diagnosis and timely intervention.
A 50-year-old female with a history of an incidentally discovered 3.4 x 1.8 cm adrenal mass was referred for evaluation of hypercortisolism (midnight salivary cortisol 0.17 μg/dL, normal < 0.09 μg/dL) with lack of suppression of both ACTH (19 pg/mL, normal 6-50 pg/mL) and cortisol (13.1 μg/dL, normal 6.0-18.4 μg/dL) on overnight 1-mg dexamethasone suppression test (DST). Pheochromocytoma work up was negative.
She denied alcohol abuse and depression screening was negative. She reported high levels of stress and insomnia. She denied muscle weakness, acne, or change to body habitus. Fasting blood glucose was intermittently as high as 212 mg/dl but HbA1c was 5.5%. She did not have a history of hypertension or glucocorticoid use. Her BMI was 20 kg/m2 and she did not appear Cushingoid. A pitutiary MRI showed no evidence of pituitary lesions or enlargement.
She was taking supplements, including biotin, and was asked to discontinue these for two weeks. Repeat 1-mg DST revealed an elevated cortisol of 9.8 μg/dL with a once again non-suppressed ACTH of 20 pg/mL. Her dexamethasone level was 109 ng/dL (normal after 1 mg dexamethasone 180-950 ng/dL), which may suggest slightly faster metabolism. All ACTH levels were run on Immulite assays, which has recently been suggested to be unreliable (1). When repeated using the Roche Assay, ACTH was low at 1.6 pg/mL. Given suppressed ACTH in conjunction with hypercortisolemia and osteoporosis, an adrenal source of CS was confirmed. Diagnosis was further solidified by a DHEA-S level of 11.4 μg/dL (normal 35.4 - 256 ug/dL). She underwent adrenalectomy and pathology revealed adrenal cortical adenomas.
The correct diagnosis of adrenal CS in this patient was delayed due to erroneously higher ACTH result by the Immulite assay. Similar cases have been reported in the literature with the use of Immulite assays for measurement of ACTH leading to invasive diagnostic procedures and even unnecessary pituitary surgery (1).
Greene LW, Geer EB, Page-Wilson G, Findling JW, Raff H. Assay-Specific Spurious ACTH Results Lead to Misdiagnosis, Unnecessary Testing, and Surgical Misadventure-A Case Series. J Endocr Soc. 2019;3(4):763-72.