This patient has features of testosterone deficiency (ie, hypogonadism), including erectile dysfunction, low libido, and gynecomastia.  His tall stature and small, firm testes are consistent with Klinefelter syndrome (KS), which causes hypogonadism due to hyalinization and fibrosis of the testes.  Patients who develop hypogonadism prior to puberty, including patients with KS, often have a eunuchoid habitus, sparse body hair, and high-pitched voice, whereas these features are much less pronounced in those who develop hypogonadism later in life.

Primary hypogonadism can be confirmed with low serum testosterone associated with elevated LH.  Management of male hypogonadism includes testosterone therapy, which can improve libido and erectile function, increase bone density, and facilitate muscle development.

(Choice A)  Aromatase inhibitors decrease the conversion of androgens to the corresponding estrogens (eg, testosterone to estradiol).  Although some experts use aromatase inhibitors as supplemental therapy in KS, the primary defect is inadequate testosterone production, so testosterone therapy should be initiated first.

(Choice B)  hCG has bioactivity analogous to that of LH and can be used to stimulate testosterone production in patients with secondary/central hypogonadism (ie, low endogenous LH).  However, patients with KS have primary hypogonadism, so gonadotropin therapy is not useful.

(Choice C)  Phosphodiesterase 5 inhibitors (eg, sildenafil) can assist in the treatment of erectile dysfunction but would not improve this patient's hormone levels or libido.

(Choice D)  Selective estrogen receptor modulators (eg, tamoxifen) are sometimes used to minimize breast enlargement in adolescents with KS.  However, nonsurgical interventions are not useful in adults with established gynecomastia.

Educational objective:
Management of male hypogonadism includes testosterone therapy, which can improve libido and erectile function, increase bone density, and facilitate muscle development.