Precocious pseudopuberty due to a rare form of congenital adrenal hyperplasia. Biochemical investigation and pitfalls in interpretation of hormone assays.

The biochemical investigation is described of a boy who presented with precocious puberty at the age of 3 years 9 months due to a rare form of congenital adrenal hyperplasia (CAH), steroid 11 beta-hydroxylase deficiency. Serum androgen levels were grossly elevated (17 hydroxyandrogens 10 nmol/l, androstenedione 129 nmol/l), 17 hydroxyprogesterone was modestly elevated (21 nmol/l), while serum gonadotrophins were low and testes were prepubertal in size. The major differential diagnosis was between an androgen-producing tumour and CAH. Initial serum and urine corticosteroid concentrations and their responses to dexamethasone were diagnostically misleading, later found to be due to lack of specificity of the radioimmunoassays and fluorimetric methods employed. Elevated basal plasma ACTH levels and suppression of androgen and ACTH levels by dexamethasone strongly suggested CAH. Definitive diagnosis of an 11 beta-hydroxylase defect was established by capillary column gas liquid chromatography of urine which demonstrated excess androgen and 11-deoxycortisol metabolites but no cortisol metabolites. The diagnosis was confirmed by specific serum assays of 11-deoxycortisol, deoxycorticosterone, and cortisol. The contribution of hormone assays and a protocol for their use in the diagnosis and monitoring of precocious puberty is discussed.