Adrenal Incidentaloma Revealing Unrecognized 21-Hydroxylase Deficiency: From Non-Classical to Late-Onset Classical Forms.

Classical congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is a rare autosomal recessive disorder. While salt-wasting forms are detected early, simple virilizing forms may remain occult until adulthood. We report two atypical cases of 21-hydroxylase deficiency revealed by adrenal incidentaloma (AI). Case 1, a 71-year-old male, presented a hypermetabolic left adrenal mass on 18FDG-PET/CT. Case 2, a 53-year-old male, showed bilateral AI on renal colic evaluation. Both patients showed significantly elevated basal 17-hydroxyprogesterone (17-OHP) and were confirmed as compound heterozygotes for CYP21A2 pathogenic variants. These cases highlight how chronic ACTH elevation in unrecognized CAH can promote adrenal nodulogenesis. Systematic 17-OHP screening in bilateral AI and hypermetabolic adrenal nodules, combined with genetic analysis, is essential for identifying late-onset classical 21-hydroxylase deficiency and preventing associated cardiometabolic and skeletal complications.