A challenging diagnosis of pediatric (cyclic) Cushing disease: the decisive role of hair cortisol.

Cushing disease is a rare and often difficult diagnosis. Therefore, a significant delay between the onset of symptoms and the final diagnosis frequently occurs. We present a previously healthy 12-year-old boy in whom hypercortisolism was suspected based on clinical symptoms: abrupt excessive weight gain despite adequate exercise and dietary interventions in combination with growth arrest. The results of conventional biochemical diagnostics for Cushing disease were contradicting and could not confirm the diagnosis. Because of a persistent clinical suspicion after a wait-and-see period, cortisol levels in the boy's 11 cm long hair were analyzed. The very high hair cortisol levels supported the clinically suspected Cushing disease. Magnetic resonance imaging of the pituitary showed evidence of an adenoma, which was confirmed postoperatively as an adrenocorticotropic hormone producing adenoma. This confirmed the diagnosis of Cushing disease, with most likely a cyclical course, 1.5 years after the initial presentation. This case adds to the scarce literature on pediatric cyclic Cushing disease and emphasizes the added value of hair cortisol.