Adult-onset idiopathic hypogonadotropic hypogonadism due to isolated pituitary gonadotropin deficiency.

A 25-year-old Japanese man with adult-onset idiopathic hypogonadotropic hypogonadism is reported. He had been delivered normally, had normal puberty, and experienced erectile dysfunction at age 24 years. Brain MRI revealed no abnormal findings and endocrinological data supported the diagnosis of isolated gonadotropin deficiency. Although most patients with idiopathic hypogonadotropic hypogonadism have a hypothalamic dysfunction, the lesion in this case may be considered to be in the pituitary since repetitive GnRH loading failed to increase serum LH and FSH.