[Diagnosis and therapy of hypogonadism in adult males]

Hypogonadism in men is defined as endocrine dysfunction of the testes, and due to reduced serum testosterone levels leads to symptoms of testosterone deficiency. Depending on the location of disruption in the endocrinological cycle, hypogonadism is classified as primary, secondary, or tertiary. In primary hypogonadism, the production of testosterone in the Leydig's cells of the testes does not function properly. Serum LH concentrations are elevated in the sense of counterregulation (hypogonadotropic hypogonadism). In secondary hypogonadism, LH secretion (and usually also FSH) from the hypophysis is impaired so that Leydig's cells are not stimulated, while in tertiary hypogonadism the hypothalamus is damaged. The clinical course in cases of reduced serum testosterone levels is determined essentially by the point in time when hypogonadism becomes manifest. Delayed puberty, eunuchoid stature, and underdeveloped secondary sex characteristics suggest prepubertal onset of hypogonadism.