The prevalence has been estimated to be 1/4000 to 1/10000 in males and 2 to 5 times less frequent in females. The prevalence difference between male and females is unknown, and is likely to be underreported for females.Acquired hypogonadotropic hypogonadism (AHH) is a postnatal onset of a GnRH releasing disorder and/or pituitary gonadotroph cell disorder. There are many causes of AHH, mostly due to structural or functional abnormalities involving the HPG axis such as sarcoidosis, lymphocytic hypophysitis, pituitary adenomas, craniopharyngiomas and other CNS tumours. Most of these patients have multiple pituitary hormone deficiencies. Hyperprolactinaemia is the most common cause of AHH. It is a well-established cause of infertility in both male and female mammals. Prolactin inhibits GnRH neurons and therefore inhibits the subsequent release of LH, FSH and sex steroids. The mechanism of prolactin induced inhibition of GnRH release is poorly understood. It is suspected that the prolactin receptor is expressed on a small subset of GnRH neurons in mice and thus has a direct inhibitory effect on GnRH release. There is evidence to suggest indirect inhibition of GnRH neurons mediated by other neurotransmitters such as dopamine, opioid, neuropeptide Y and γ-aminobutyric acid. Drug usage of glucocorticoids and opioid analgesics in high dosages can lead to the inhibition of GnRH synthesis. Opioid receptors reside in the hypothalamus and when bound to opioids they decrease the normal pulsatile secretion of GnRH and therefore result in HH.
Chronic treatment with supraphysiological doses of glucocorticoids results in a marked decrease in testosterone without an increase of LH levels, suggestive of a central mechanism of induced HH. Diagnosis
The clinical presentation of HH depend on the time of onset as well as the severity of the defect. Diagnostic tests to measure GnRH levels are difficult. This is because GnRH is confined within hypophyseal portal system and has a short half-life of 2–4 minutes. GnRH levels are thus checked indirectly via LH and FSH levels which will be totally or partially absent in HH. Exogenous GnRH can be used as a diagnostic tool. If the patient has hypothalamic GnRH deficiency, LH and FSH will gradually appear in response to the exogenous GnRH but in pituitary cases of HH, a minimal response will be generated. Typically, CHH is diagnosed in adolescence due to a lack of pubertal development, but it can be possible to diagnose in male neonates. Clinical presentations of CHH involve an absence of puberty by 18 years of age, poorly developed secondary sexual characteristics, or infertility.In men with CHH, serum levels of inhibin B are typically very low as inhibin B is a marker of Sertoli cell number. For females, CHH is most commonly revealed by primary amenorrhea. Breast development is variable and pubic hair may or may not be present. CHH can be diagnosed in the male neonate with cryptorchidism (maldescended testes) and a micropenis as signs of GnRH deficiency. There are no clear signs of CHH in female neonates.