Unilateral testicular enlargement resulting from inapparent 21-hydroxylase deficiency

We report a case in which unilateral testicular enlargement was the only presenting sign in 21-hydroxylase deficiency of the "acquired" or adult onset type. Measurement of plasma 17-hydroxyprogesterone throughout 24 hours revealed marked elevations, mostly between 0400 and 0700 hours. However, this steroid increased more than 18-fold 30 minutes following adrenocorticotropic hormone administration, confirming the diagnosis. Glucocorticoid therapy corrected the testicular enlargement. Inapparent 21-hydroxylase deficiency is a medically treatable cause of testicular enlargement that can be diagnosed by measurement of plasma 17-hydroxyprogesterone during a 30-minute adrenocorticotropic hormone stimulation test.