Pitfall of Petrosal Sinus Sampling in a Cushing’s Syndrome Secondary to Ectopic Adrenocorticotropin-Corticotropin Releasing Hormone (ACTH-CRH) Secretion

THE diagnosis evaluation of ACTH-dependent Cushing’s syndrome (CS) can be a challenge for the physician. Distinguishing between a pituitary adenoma of Cushing’s disease (CD) and an ectopic ACTH-producing tumor is very often difficult. Patients with either tumor may respond similarly to routine tests such as high-dose dexamethasone suppression or metyrapone test. In addition, the small size of most ACTH-secreting pituitary microadenomas and many ectopic ACTH-producing tumors may cause false negative imaging results. Thus, over the past ten years, inferior petrosal sinus (IPS) sampling has been proposed as the gold standard for the differential diagnosis between pituitary and nonpituitary ACTH-dependent CS. With the adjunctive use of corticotropin releasing hormone (CRH), the diagnostic accuracy of this test reaches almost 100% (1). The present report demonstrates that IPS sampling with CRH stimulation has not the same reliability in case of concomitant ectopic ACTH-CRH secretion. A 60-yr-old man was referred for evaluation of CS. He presented with a 12-month history of 12 kg weight gain, muscular weakness, and hypertension. Physical examination revealed truncal obesity, redness of the face, moon facies, buffalo hump, and supraclavicular fossa fullness, but no purple striae. He had severe proximal muscular atrophy, several small ecchymotic areas over the extremities, and skin atrophy, but no melanodermia. Blood pressure was 190/110 mm Hg. Routine laboratory studies performed on admission showed hyperglycemia (glucose concentration: 11 mmol/L), hypokalemia (potassium: 2.7 mmol/L), and metabolic alcalosis (bicarbonate: 31 mmol/L). CS was confirmed on elevated free urinary cortisol, lack of plasma cortisol circadian rhythm, and resistance to the 2-day low-dose (2 mg) dexamethasone test (Table 1).