LH deficiency, decreased LH
Low level of luteinizing hormone (LH) refers to levels under normal serum concentration. An isolated LH deficiency is not a common condition. As LH is secreted as pulses (Pic. 1), it is necessary to follow its concentration over a sufficient period of time to get proper information about its blood levels. During the reproductive years, typical levels in women are between 1–20 IU/L. In males over 18 years of age, reference ranges have been estimated to be 1.8–8.6 IU/L (Pic. 2). LH levels are normally low during childhood and in postmenopausal women.
LH deficiency almost always occurs in conjunction with follicle-stimulating hormone (FSH) deficiency because LH and FSH are secreted by the same pituitary gonadotrope cells. The underlying cause of the failure in production of LH and FSH can be:
1) Hypothalamic insuficiency
The impairment of the hypothalamus (a part of the brain, responsible for the control of secretion of most hormones) to release the hormone gonadotropin-releasing hormone (GnRH) which in normal circumstances induces the production of LH and FSH (Pic. 3). Without the correct release of GnRH the pituitary gland is unable to release LH and FSH which in turn prevents the ovaries and testes from functioning correctly. This failure in GnRH production can either be due to the absence of the GnRH releasing neurones inside the hypothalamus or the inability of the hypothalamus to release GnRH in the correct pulsatile manner to ensure LH and FSH release from the pituitary.
2) Pituitary insufficiency (hypopituitarism)
Reduced ability of the pituitary gland to release LH and FSH. If the reduced secretion affects only specific hormones, the condition is termed hypopituitarism. If all pituitary hormones are affected, it is known as panhypopituitarism. The pathophysiology of hypopituitarism mainly involves ischemic injury (damage due to reduced blood flow) of the pituitary gland. The ischemia may be due to hemorrhage, tumors, brain injury, and compression or occlusion of the hypophyseal blood vessels.
Diminished secretion of LH can result in failure of gonadal function (hypogonadism). The subtype of hypogonadism where LH and FSH levels are low is specifically called hypogonadotropic hypogonadism. This condition is typically manifest in males as failure in production of normal numbers of sperm. In females, amenorrhea (cessation of menstrual cycle) is commonly observed.
Conditions of low LH secretion, usually paired with low FSH secretion, include Kallman syndrome, suppression of hypothalamus, hypopituitarism, eating disorders, female athlete triad (eating disorders, amenorrhea and osteoporosis), hyperprolactemia (elevated levels of prolactin), Pasqualini syndrome (also called fertile eunuch syndrome) and gonadal supression therapy.
Low level of LH may be associated with several conditions, including:
Kallmann syndrome is a condition characterized by delayed or absent puberty and an disturbed sense of smell. It represents a form of hypogonadotropic hypogonadism, as the gonadotropin (LH and FSH) levels are usually low. In Kallmann syndrome, the sense of smell is either diminished (hyposmia) or completely absent (anosmia). This feature distinguishes Kallmann syndrome from most other forms of hypogonadotropic hypogonadism, which do not affect the sense of smell. The features of Kallmann syndrome vary, even among affected people in the same family. Additional signs and symptoms can include a failure of one kidney to develop (unilateral renal agenesis), a cleft lip with or without an opening in the roof of the mouth (a cleft palate), abnormal eye movements, hearing loss, and abnormalities of tooth development. Some affected individuals have a condition called bimanual synkinesis, in which the movements of one hand are mirrored by the other hand.
Pasqualini syndrome, fertile eunuch syndrome
The fertile eunuch syndrome is a cause of hypogonadotropic hypogonadism caused by a luteinizing hormone deficiency. It is characterized by hypogonadism with spermatogenesis. The patients exhibit a eunuchoid appearance, but have healthy testes and functional spermatogenesis, and are usually fertile. Therefore, they are not really eunuchs, and the term „eunuch syndrome“ is incorrect and should not be used.
Hypopituitarism is the condition of deficiency of one or more anterior and/or posterior pituitary hormones. Hypopituitarism is referred to the deficiency of one of the pituitary gland hormones or more while the deficiency of all pituitary hormones is known as panhypopituitarism. Clinical presentation in hypopituitarism depends upon the onset, the severity of hormonal deficiency and the number of deficient hormones. Patients with hypopituitarism are ill-appearing and usually look tired. Gonadotropin deficiency may present with breast atrophy, soft testes, and regression of sexual characteristics.
Female athlete triad
Female athlete triad is a syndrome in which eating disorders (or low energy availability), amenorrhoea/oligomenorrhoea, and decreased bone mineral density (osteoporosis and osteopenia) are present. Also known simply as the Triad, this condition is seen in females participating in sports that emphasize leanness or low body weight. The triad is a serious illness with lifelong health consequences and can potentially be fatal. The underlying cause of the female athlete triad is an imbalance between energy taken into the body (through nutrition) and energy used by the body (through exercise). Clinical symptoms of the Triad may include disordered eating, fatigue, hair loss, cold hands and feet, dry skin, noticeable weight loss, increased healing time from injuries (e.g., lingering bruises), increased incidence of bone fracture and cessation of menses. Affected females may also struggle with low self-esteem and depression.