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ESSENTIALS OF DIAGNOSIS

  • Diminished libido and erections.

  • Fatigue, depression, reduced exercise endurance.

  • Decreased growth of body hair.

  • Testes small or normal in size.

  • Low serum total testosterone or free testosterone.

  • Serum LH and FSH are low or normal in hypogonadotropic hypogonadism; they are high in testicular failure (hypergonadotropic hypogonadism).

GENERAL CONSIDERATIONS

Male hypogonadism is caused by deficient testosterone secretion by the testes. It may be classified according to whether it is due to (1) insufficient gonadotropin secretion by the pituitary (hypogonadotropic); (2) pathology in the testes themselves (hypergonadotropic); or (3) both (Table 26–12). Partial male hypogonadism may be difficult to distinguish from the physiologic reduction in serum testosterone seen in normal aging, obesity, and illness.

Table 26–12.Causes of male hypogonadism.

ETIOLOGY

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, with causes including isolated hypogonadotropic hypogonadism, hypopituitarism, or simple constitutional delay of growth and puberty; or it can be acquired, with causes listed in Table 26–12. Genetic conditions (eg, Kallmann syndrome or PROKR2 mutations, X-linked congenital adrenal hypoplasia, 17-ketosteroid reductase deficiency, Prader-Willis syndrome) account for about 40% of cases of isolated, and apparently idiopathic, acquired hypogonadotropic hypogonadism with a serum testosterone level less than 150 ng/dL (5.2 nmol/L).

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. 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 26–12. Male hypergonadotropic hypogonadism can also be caused by XY gonadal dysgenesis, partial 17-ketosteroid reductase deficiency and a congenital partial deficiency in the steroidogenic enzyme CYP17 ...

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