A 55-year-old man with a known adrenal incidentaloma undergoes a 1 mg overnight dexamethasone suppression test. His 8 AM cortisol is 4.5 µg/dL (normal <1.8 µg/dL). He has no Cushingoid features. What does this finding most likely represent?

• A Overt Cushing's syndrome requiring immediate treatment
• B Normal variant — dexamethasone suppression is unreliable with incidentalomas
• C Pseudo-Cushing state from obesity — repeat testing after weight loss
• D Autonomous cortisol secretion (mild autonomous cortisol secretion, previously called 'subclinical Cushing's'), associated with metabolic risk ✓

Explanation

A post-dexamethasone cortisol >1.8 µg/dL indicates non-suppression, but the absence of overt clinical features defines this as mild/autonomous cortisol secretion (MACS), formerly 'subclinical Cushing's.' These patients have increased risks of hypertension, type 2 diabetes, dyslipidemia, osteoporosis, and cardiovascular events. Further evaluation with 24-hour UFC and late-night salivary cortisol is warranted. Overt Cushing's has both biochemical and clinical manifestations. Pseudo-Cushing (depression, alcoholism, obesity) also impairs DST but is excluded by the incidentaloma context and requires clinical correlation.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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