Introduction: Cushing’s disease in adolescents is rare and frequently difficult to diagnose due to overlapping features with common pubertal and metabolic conditions. We present an adolescent who underwent inferior petrosal sinus sampling (IPSS) with possible cyclical Cushing’s disease, highlighting the diagnostic challenges and the interpretive value of IPSS. Case: A 16-year-old female presented with progressive weight gain, acne, hirsutism, secondary amenorrhea, proximal myopathy, violaceous striae, and facial plethora over 1 year. Her 24-hour urinary cortisol was >3,310 nmol/L with failure of suppression following a 1-mg overnight dexamethasone suppression test (701 nmol/L). Her adrenocorticotropic hormone (ACTH) was raised (77.9 pg/mL), consistent with ACTH-dependent Cushing syndrome. Her hemoglobin A1c was 5.9%, and she has low bone mass for age with a Z score of -2.9 at the Lumbar spine. Pituitary magnetic resonance imaging identified a rightsided microadenoma measuring 0.6 × 0.5 cm, while computed tomography of the thorax, abdomen, and pelvis showed no ectopic source. IPSS with desmopressin stimulation was performed to confirm the ACTH source. No steroidogenesis inhibitors were administered prior to testing. Notably, cortisol levels during IPSS were relatively low, with midnight cortisol of 91 nmol/L and morning cortisol of 200 nmol/L, suggesting testing during a trough phase of possible cyclical hypercortisolism. Despite this, IPSS demonstrated a significant central-to-peripheral ACTH gradient supporting a pituitary source. Conclusion This case highlights the diagnostic dilemma of interpreting IPSS in suspected cyclical Cushing’s disease. Fluctuating cortisol secretion may result in discordant biochemical findings and complicate localization studies. IPSS findings should be interpreted cautiously and integrated with clinical features, imaging, and serial biochemical monitoring. Recognition of cyclical disease patterns is essential to ensure appropriate management in adolescent patients.
Adolescent ; Humans ; Petrosal Sinus Sampling