A 25 year old Chinese young lady was referred to Endocrinology clinic in view of subclinical hyperthyroidism (fT4 12.4, TSH 0.054) picked up incidentally by her dermatologist who was seeing her for oily skin and alopecia. Although she had no symptoms or signs of hyperthyroidism, she was noted to be Cushingoid in appearance - she had rounded facies, supraclavicular adipose tissue, thin limbs and thin skin with easy bruising. Her BMI was however only 19 kg/m2 and did not have abdominal striae, hirsutism or proximal myopathy. She was hypertensive with a blood pressure of 150/110 mmHg. In view of these features, screening for Cushing's syndrome was done: 1mg overnight dexamethasone suppression test (ONDST) revealed cortisol was not suppressed (615nmol/L), and 24h urine free cortisol (UFC) was raised at 2233 nmol/day (5.4x upper limit of normal). Corresponding ACTH was low (2.8 ng/L), confirming ACTH-independent Cushing’s. However, both CT and MRI adrenals showed normal adrenals with no masses.
Suspicion at this point was that of primary pigmented nodular adrenal hyperplasia (PPNAD) in view of her young age, ACTH independent Cushing's syndrome and lack of adrenal mass found on imaging. Liddle's test was done: