Lymphocytic (Autoimmune) Hypophysitis
- A rare autoimmune disease that occurs when the pituitary gland is infiltrated with lymphocytes and plasma cells, leading to impaired hormonal secretion
- Patients present with varying degrees of pituitary hormonal impairment or enlargement.
- Cause is usually unknown.
- The most common form affects the anterior pituitary and causes hypopituitarism.
- Less commonly affects the infundibulum or posterior pituitary, causing diabetes insipidus and hyperprolactinemia
- Predominantly seen in women: female > male (5:1)
- Strong association with pregnancy, most frequently occurring in the gestational or postpartum period, but cases outside of pregnancy are increasingly seen
- Females tend to present at a younger age (35 years) than do males (45 years).
- Annual incidence estimated at 1 case per 9 million
- Increasingly becoming more recognized
- Thought to be underestimated because of the following:
- Frequency of case reports are increasing.
- Undiagnosed cases due to indolent disease
- Found in <1% of all surgical pituitary samples
Etiology and Pathophysiology
- Most commonly caused by an autoimmune infiltration that includes an admixture of T and B lymphocytes with plasma cells
- Causes extrasellar pituitary enlargement
- CD8 T cells mediate the attack on pituitary cells.
- Antipituitary antibodies are considered markers of the T-cell mediation and are detectable in serum.
- It is unknown if antipituitary antibodies play a pathogenic role.
- Can also be caused by an inflammatory process
- Initially leads to symptoms consistent with a pituitary mass effect (similar to pituitary adenoma)
- Followed by fibrosis and shrinkage, causing differing degrees of hypopituitarism
- Extension of the inflammatory process into the posterior pituitary and up into the neurohypophysis leads to diabetes insipidus, which is more common in males.
- With complete progression, panhypopituitarism occurs with an empty sella turcica.
- Patients often have family history of autoimmunity.
- HLA DR4 allele, HLA DR5 allele (DR4 > DR5)
- Recent association found with HLA DQ8 and DR53 alleles as well
- Can be associated with antibody to PIT1 (POU1F1)
- Female gender
- Pregnant type 1 diabetics are at even higher risk.
- Personal or family history of autoimmune disease
- May be associated with viral infections, particularly meningoencephalitis
- CTLA-4 antibody cancer treatment (e.g., ipilimumab or tremelimumab)
Commonly Associated Conditions
- Aseptic meningitis: unknown if simple association or causal
- Other autoimmune polyendocrinopathies are the following:
- Hashimoto thyroiditis; Graves disease is most common.
- Addison disease, type 1 diabetes mellitus, central diabetes insipidus, chronic atrophic gastritis, polyglandular autoimmune disease type 1 and type 3, systemic lupus erythematosus, Sjögren syndrome, autoimmune hepatitis, pernicious anemia, and primary biliary cirrhosis
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