Male Hypogonadism: Male Reproductive Endocrinology: Merck …

(See also Male Hypogonadism in Children.)

Hypogonadism is defined as testosterone deficiency with associated symptoms or signs, deficiency of spermatozoa production, or both. It may result from a disorder of the testes (primary hypogonadism) or of the hypothalamic-pituitary axis (secondary hypogonadism). Both may be congenital or acquired as the result of aging, disease, drugs, or other factors. Additionally, a number of congenital enzyme deficiencies cause varying degrees of target organ androgen resistance. Diagnosis is confirmed by hormone levels. Treatment varies with etiology but typically includes gonadotropin-releasing hormone, gonadotropin, or testosterone replacement.

Primary hypogonadism involves failure of the testes to respond to follicle-stimulating hormone (FSH) and luteinizing hormone (LH). When primary hypogonadism affects testosterone production, testosterone is insufficient to inhibit production of FSH and LH; hence, FSH and LH levels are elevated. The most common cause of primary hypogonadism is Klinefelter syndrome. It involves seminiferous tubule dysgenesis and a 47,XXY karyotype (see Klinefelter Syndrome (47,XXY)).

Secondary hypogonadism is failure of the hypothalamus to produce gonadotropin-releasing hormone (GnRH) or of the pituitary gland to produce enough FSH and LH. In secondary hypogonadism, testosterone levels are low and levels of FSH and LH are low or inappropriately normal. Any acute systemic illness can cause temporary secondary hypogonadism. Some syndromes of hypogonadism have both primary and secondary causes (mixed hypogonadism). Table 1: Causes of Hypogonadism* lists some common causes of hypogonadism by category.

Some syndromes of hypogonadism (eg, cryptorchidism, some systemic disorders) affect spermatozoon production more than testosterone levels.

Table 1

Type

Congenital Causes

Acquired Causes

Primary (testicular)

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Male Hypogonadism: Male Reproductive Endocrinology: Merck ...

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