This article describes autoimmune pituitary gland impairment, a condition that can be fatal in pregnancy and during the postpartum period.
Hypophysitis is a collective term for disorders of impaired pituitary gland function. Autoimmune hypophysitis (AH), which is also known as lymphocytic hypophysitis or lymphocytic adenohypophysisitis, is a rare autoimmune disease characterized by inflammation and impaired function of the anterior region, the infundibular stem, or the posterior lobe of the pituitary gland. AH is the most common cause of primary hypophysitis and pituitary gland inflammation.
In AH more than one region of the pituitary gland may be affected. The pituitary gland may also be enlarged if inflammation is pronounced. In AH the pituitary gland is infiltrated by white blood cells, primarily lymphocytes, plasma cells and macrophages. Because the pituitary gland regulates the function of other endocrine glands, hypohysitis is often accompanied by one or more other endocrine disorders usually adrenal insufficiency. Autoimmune hypophysitis is most likely to occur during pregnancy or the postpartum period although it can rarely occur in pre-pubertal and post-menopausal females and in men.
Although earlier cases undoubtedly exist, the first case of AH was reported in 1980. Since, most incidences of AH have been reported in women during the last month of pregnancy or the second month after delivery. Of all the autoimmune diseases, AH has the strongest association with pregnancy. Normally, the pituitary gland increases about 30 percent during pregnancy primarily due to the estrogen-induced increase in cells that produce hormones needed for lactation. Changes related to estrogen also cause increased systemic blood flow to the pituitary. These changes are suspected of triggering AH but they have not been conclusively proven.
SYMPTOMS AND SIGNS
Symptoms in hypophysitis include headache, increased secretion of the hormone prolactin, visual field impairment, blood sugar disturbances, and double vision. The signs of AH include sellar (interior of the pituitary gland) compression, decreased pituitary function (hypopituitarism), diabetes insipidus, central hypothyridism, and hyperprolactinemia (increased secretion of the lactation hormone prolactin).
Sellar compression causes headache and visual disturbances including double vision. These are usually the initial symptoms that occur. Headache is related to distension and distortion of the brain's dura mater and diaphragma sellae by the expanding pituitary mass. Later symptoms related to partial or complete deficit of the anterior pituitary hormones are considered due to the autoimmune destruction of the pituitary gland's acinar cells. Hormone deficiencies cause symptoms related to hypoadrenalism, hypothyroidism, and hypogonadism. Decreased lactate production causes an inability to lactate in the postpartum period.
Still later symptoms are related to deficits of the posterior pituitary gland and include diabetes insipidus, which may be masked by a co-existing glucocorticoid deficiency. Symptoms of hyperprolactinemia include amenorrhea (scant or absent menstrual periods) and galactorrhea, Fatalities in mothers have occurred during late pregnancy and during delivery with no apparent harm to the fetus. During pregnancy symptoms escalate faster. Outside of pregnancy, symptoms may occur for 6-7 months before the signs of AH become noticeable. The predominant symptoms vary according to the region of the pituitary gland that's affected.
DIAGNOSIS
Imaging tests are used to rule out the possibility of endocrine tumor, granulomas, and xanthomatous cysts. MRI findings in LH include a symmetric enlargement of the pituitary gland, a thickened but rarely displaced stalk and a usually intact sellar floor. If surgical samples are available, tissue studies are used to diagnose and further classify AH. The defining characteristic of AH is the lymphocytic infiltration of the pituitary gland. At presentation the cortisol producing cells are the most frequently impaired, followed by the thyrotroph cells that produce TSH (causing central hypothyroidism due to inadequate TSH; TSH causes thyroid hormone production), and later by the somatotrophs, lactotrophs, and gonadotrophs, which are cells that produce sleep, lactation and reproductive hormones.
Diagnosis is suspected, most commonly during pregnancy and in the postpartum period, when symptoms of hypopituitarism occur and appear disproportionate to the relatively small size of the pituitary mass. The adrenal and thyroid axes are also more likely to be affected in AH compared to hypophysisis of other primary or secondary causes.
TREATMENT
Treatment for AH is primarily used to reduce symptoms, correct hormonal imbalances with replacement hormone, an reduce the size of he pituitary mass with pituitary surgery, glucocorticoids, azathioprine, methotrexate or radiotherapy. Most patients have surgery, which reduces congestion through decompression and allows for histological studies of the removed tissue. With surgery, headaches and visual disturbances typically resolve or improve. Glucocorticoid steroids effectively reduce inflammation and replace deficient hormone.
Resources:
Patrizio Caturegli, Craig Newschaffer, Alessandro Olivi, Martin Pomper, Peter Burger and Noel Rose, Autoimmune Hypophysitis, Endocrine Reviews, 2005 26(5):599-614.
Antonio Bellastella, Antonio Bizzarro, Lymphocytic hypophysitis: a rare or underestimated disease? European Journal of Endocrinology, 2003, 149: 363-376
