Vanishing 17-Hydroxyprogesterone Concentrations in 21-Hydroxylase Deficiency.

We present a boy with a genetically proven congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency. While massively elevated 17-hydroxyprogesterone (17-OHP) concentrations after birth led to the diagnosis, 17-OHP concentrations became immeasurable starting with the second year of life even though the dose of hydrocortisone was continuously decreased to ∼7 mg/m2/day. Furthermore, 17-OHP levels were immeasurable during the ACTH test and after withdrawing hydrocortisone medication. In contrast, ACTH levels increased after cessation of hydrocortisone treatment suggesting complete primary adrenal cortex failure. We discuss this case based on the differential diagnosis of complete adrenal cortex failure including other genetic causes in addition to CAH, prednisolone treatment, autoimmune adrenalitis, adrenoleukodystrophy, CMV infection, and adrenal hemorrhage infarction. The most likely disease in our boy is autoimmune adrenalitis, which is difficult to prove years after the onset of the disease. Treatment of CAH had masked the classical symptoms of complete adrenal cortex insufficiency leading to delayed diagnosis in this case.