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  • Diminished libido and erections.

  • Fatigue, depression, reduced exercise endurance.

  • Testes small or normal in size.

  • Low serum total testosterone or free testosterone.

  • Hypogonadotropic hypogonadism: low or normal serum LH and FSH.

  • Hypergonadotropic hypogonadism: testicular failure, high serum LH and FSH.


Male hypogonadism is caused by deficient testosterone secretion by the testes. It may be due to (1) insufficient gonadotropin secretion by the pituitary (hypogonadotropic); (2) pathology in the testes (hypergonadotropic); or (3) both (Table 26–13). Partial male hypogonadism may be difficult to distinguish from the physiologic reduction in serum testosterone seen in normal aging, obesity, and illness.

Table 26–13.Causes of male hypogonadism.


A. Hypogonadotropic Hypogonadism (Low Testosterone with Normal or Low LH)

A deficiency in FSH and LH may be isolated or associated with other pituitary hormonal abnormalities. (See Hypopituitarism.) Hypogonadotropic hypogonadism can be primary, defined as failure to enter puberty by age 14, or it can be acquired. Causes of primary hypogonadotropic hypogonadism include hypopituitarism, isolated hypogonadotropic hypogonadism, or simple constitutional delay of growth and puberty. Causes of acquired hypogonadotropic hypogonadism include genetic conditions (eg, Kallmann syndrome or PROKR2 mutations, X-linked congenital adrenal hypoplasia, 17-ketosteroid reductase deficiency, Prader-Willis syndrome), which account for about 40% of cases of isolated and idiopathic disease with a serum testosterone level less than 150 ng/dL (5.2 nmol/L) (Table 26–13).

Partial male hypogonadotropic hypogonadism is defined as a serum testosterone in the range of 150–300 ng/dL (5.2–10.4 nmol/L). The main causes of acquired partial male hypogonadotropic hypogonadism include obesity, poor health, or normal aging, such that it is termed age-related hypogonadism. However, other causes need to be excluded, including pituitary or hypothalamic tumors. Spermatogenesis is usually preserved.

B. Hypergonadotropic Hypogonadism (Testicular Failure with High LH)

A failure of the testicular Leydig cells to secrete adequate testosterone causes a rise in LH and FSH. Acquired conditions that can cause testicular failure are listed in Table 26–13. Male hypergonadotropic hypogonadism can be caused by ...

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