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Sheehan's syndrome, also known as postpartum pituitary gland necrosis, is hypopituitarism (decreased functioning of the pituitary gland), caused by ischemic necrosis due to blood loss and hypovolemic shock during and after childbirth.

Signs and symptoms
The various signs and symptoms in Sheehan's syndrome are caused by damage to the pituitary, thereby causing a decrease in one or more hormones it normally secretes. Since the pituitary controls many glands in the endocrine system, partial or complete loss of a variety of functions may result.

Most common initial symptoms of Sheehan's syndrome are agalactorrhea (absence of lactation) and/or difficulties with lactation. Many women also report amenorrhea or oligomenorrhea after delivery. In some cases, a woman with Sheehan syndrome might be relatively asymptomatic, and the diagnosis is not made until years later, with features of hypopituitarism. Such features include secondary hypothyroidism with tiredness, intolerance to cold, constipation, weight gain, hair loss and slowed thinking, as well as a slowed heart rate and low blood pressure. Another such feature is secondary adrenal insufficiency, which, in the rather chronic case is similar to Addison's disease with symptoms including fatigue, weight loss, hypoglycemia (low blood sugar levels), anemia and hyponatremia (low sodium levels). Such a woman may, however, become acutely exacerbated when her body is stressed by, for example, a severe infection or surgery years after her delivery, a condition equivalent with an Addisonian crisis. The symptoms of adrenal crisis should be treated immediately and can be life-threatening. Gonadotropin deficiency will often cause amenorrhea, oligomenorrhea, hot flashes, or decreased libido. Cessation of menses is an important indicator of Gonadotropin deficiency as a result of Sheehan’s syndrome. Growth hormone deficiency causes many vague symptoms including fatigue and decreased muscle mass.

Growth hormone deficiency is the most common symptom of hypopituitarism seen in Sheehan’s syndrome with a 90%-100% occurrence seen in the Netherlands, Costa Rica, and Saudi Arabia. In these populations the occurrence of Cortisol, TSH, and gonadotropin deficiencies ranges from 50 to 100%.

Uncommonly, Sheehan syndrome may also appear acutely after delivery, mainly by hyponatremia. There are several possible mechanisms by which hypopituitarism can result in hyponatremia, including decreased free-water clearance by hypothyroidism, direct syndrome of inappropriate antidiuretic hormone (ADH) hypersecretion, decreased free-water clearance by glucocorticoid deficiency (independent of ADH). The potassium level in these situations is normal, because adrenal production of aldosterone is not dependent on the pituitary.

Causes
In the developed world it is a rare complication of pregnancy, usually occurring after excessive blood loss after delivery. The presence of disseminated intravascular coagulation (i.e., in amniotic fluid embolism or HELLP syndrome) also appears to be a factor in its development. A retrospective study in turkey found that the prevalence of Sheehan’s syndrome was directly proportional the amount of at-home deliveries each decade

Pituitary necrosis may directly result from a lack of blood flow in the hypophyseal artery as a result of pituitary gland enlargement during pregnancy. Ischemia may occur as a result of vasospasm, thrombosis , or vascular compression sometimes as a result of an increase in the amount of lactotroph cells throughout gestation (contributing to the enlargement of the pituitary gland). Necrosis may occur as a result of severe hypotension or shock due to excessive uterine bleeding following childbirth. . Sheehan’s syndrome may occur as a result of the arterial constriction and abnormal hypotension in conjunction with an insufficiency to meet the increased demand in blood supply of the pituitary gland seen during pregnancy.

Some possible predisposing factors to Sheehan’s syndrome may include: inherited or acquired disseminated blood coagulation (DIC) restriction pituitary blood supply, small sella size, vasospasm, or thrombosis. Post-Partum Hemorrhaging (PPH) is believed to be a predictor of Sheehan’s syndrome, so factors that may increase the chance of PPH such as: anaemia, obesity, and advanced maternal age) may increase the risk of Sheehan Syndrome.

Pathophysiology
Sheehan's syndrome is caused by damage to the pituitary, thereby causing a decrease in one or more hormones it normally secretes. Secondly, the anterior pituitary is supplied by a low pressure portal venous system.[ medical citation needed] A 1995 study found that 56.2% of patients with diagnosed Sheehan’s syndrome experienced a loss of all pituitary hormones (with the remaining 43.8% having selective pituitary insufficiency). However, likely because the growth hormone-secreting cells are located at the periphery of the pituitary (and are therefore most likely to be affected by ischemia), all the patients had growth hormone deficiency. undefined

Diagnosis
Hormonal assays: there may be low level of T4, TSH, estrogen, gonadotropin, cortisol and ACTH depending on the extent of necrosis

MRI of the pituitary and hypothalamus: this helps to exclude tumor or other pathologies.

Treatment
Life long hormone replacement therapy for the hormones that are missing.

Epidemiology
In a study of 1,034 symptomatic adults, Sheehan syndrome was found to be the sixth most frequent etiology of growth hormone deficiency, being responsible for 3.1% of cases (versus 53.9% due to a pituitary tumor).

Sheehan syndrome is more prevalent in developing countries than developed countries. Additionally, it was found that the majority of women who experienced Sheehan syndrome gave birth at home.

History
The specific association with postpartum shock or haemorrhage was described in 1937 by the British pathologist Harold Leeming Sheehan (1900–1988), whereas Simmonds' disease occurs in either sex due to causes unrelated to pregnancy.

According to Sheehan in 1939 approximately 41% of survivors of severe postpartum hemorrhage (PPH) and/or hypovolemic shock experienced severe or partial hypopituitarism.