Hypopituitarism

Hypopituitarism is a medical term describing deficiency (hypo) of one or more hormones of the pituitary gland. The pituitary produces a number of important regulating hormones, and its function is mainly regulated by the hypothalamus. In endocrinology, deficiency of multiple hormones of the anterior lobe is generally referred to as hypopituitarism, while deficiency of the posterior lobe generally only leads to diabetes insipidus. If both lobes malfunction, the term panhypopituitarism (generalised hypopituitarism) is used.

Physiology
The primary hormones of the anterior pituitary are proteins and include These hormones are secreted in individually characteristic pulsatile patterns, often with distinct circadian rhythm, rather than at steady rates throughout 24 hours.
 * growth hormone (GH) - growth and glucose homeostasis
 * luteinizing hormone (LH) - menstrual cycle and reproduction
 * follicle stimulating hormone (FSH) - same
 * adrenocorticotropic hormone (ACTH) - stimulates glucocorticoid production in the adrenal gland
 * thyroid stimulating hormone (TSH) - stimulates thyroxine production in the thyroid
 * prolactin (PRL) - stimulates milk production in the breast

The posterior pituitary produces antidiuretic hormone (ADH) and oxytocin, the former regulating plasma osmolarity and the latter regulating uterine contractions during childbirth.

Growth hormone is often the first hormone lost, so most people with hypopituitarism lack GH as well as one or more others. As for the posterior pituitary, ADH deficiency is the main problem, while oxytocin deficiency rarely causes clinically significant problems.

Causes
Hypopituitarism and panhypopituitarism can be congenital or acquired. A partial list of causes and forms:
 * Congenital hypopituitarism
 * Hypoplasia of the pituitary
 * Isolated idiopathic congenital hypopituitarism
 * Associated with other congenital syndromes and birth defects
 * Septo-optic dysplasia
 * Holoprosencephaly
 * Chromosome 22 deletion syndrome
 * Rapaport syndrome
 * Single gene defect forms of anterior pituitary hormone deficiency
 * Acquired hypopituitarism
 * trauma (e.g., skull base fracture)
 * surgery (e.g., removal of pituitary neoplasm)
 * tumor (secretory and non-secretory pituitary or hypothalamic neoplasms)
 * inflammation (e.g. sarcoidosis or autoimmune hypohysitis)
 * radiation (e.g., after cranial irradiation for childhood leukemia)
 * shock
 * (Sheehan's syndrome is hypopituitarism after heavy bleeding in childbirth)
 * hemochromatosis
 * other diseases.

Diagnosis
Hypopituitarism may come to medical attention by symptoms or features of pituitary hormone deficiency (e.g., poor growth, hypoglycemia, micropenis, delayed puberty, polyuria, impaired libido, fatigue, and many others), or because the physician has diagnosed one of the many disorders and conditions associated with hypopituitarism listed above and tests for it.

Replacement therapy
Hypopituitarism and panhypopituitarism are treated by replacement of appropriate hormones. Since the most of the anterior pituitary hormones are proteins released in pulsatile patterns, whose functions are to induce secretion of smaller molecule hormones (thyroid hormones and steroids), it is simpler and less expensive for most purposes to simply replace the target gland hormones. There are a few exceptions, such as fertility induction.
 * GH is replaced with growth hormone.
 * TSH is replaced with thyroxine.
 * ACTH is usually replaced with hydrocortisone but any glucocorticoid may be used.
 * LH and FSH are most often replaced by supplying the appropriate sex steroids (e.g., testosterone or estrogen and progestin). Virtually all people who need T or E2 replacement for hypopituitarism rarely have spontaneous, effective spermatogenesis or follicular maturation. Both GnRH by subcutaneous pump and gonadotropins (Pergonal) by daily subcutaneous injections have been used effectively to induce fertility.
 * Prolactin is not usually replaced, as infant formula is readily available, simpler, and much cheaper.
 * ADH is replaced most commonly with oral, nasal, and sometimes intravenous or subcutaneous desmopressin.
 * Oxytocin is most important during labor and delivery at the end of pregnancy, and can be replaced in that circumstance by pitressin.