Chapter 45 – Autoimmune Hypophysitis

Autoimmune hypophysitis is a chronic inflammation of the pituitary gland that can be classified according to anatomic location, histopathology, or cause. Location differentiates hypophysitis into adenohypophysitis, infundibulo-neurohypophysitis, or panhypophysitis depending on whether the clinical and radiological signs (and pathological findings if available) involve the anterior lobe, the posterior lobe and the stalk, or both structures. Histopathology identifies two main forms of hypophysitis, lymphocytic and granulomatous, as well as xanthomatous, IgG4 plasmacytic, and necrotizing variants. Etiology distinguishes primary and secondary hypophysitis. Primary hypophysitis refers to the cases that do not currently have an identifiable cause. It is the most common form of hypophysitis, has an autoimmune pathogenesis, and occurs in isolation or with other well-characterized autoimmune diseases. Secondary hypophysitis includes the cases where a clear etiological agent can be identified (for example, the administration of immunomodulatory drugs like CTLA-4 blocking antibody), the cases where the inflammation of the pituitary is considered a reaction to sellar diseases (Rathke’s cleft cyst, craniopharyngioma, germinoma, and pituitary adenomas), and the cases where hypophysitis is part of a multiorgan systemic involvement (such as Wegener’s granulomatosis, tuberculosis, sarcoidosis, or syphilis). In this chapter is discussed predominantly primary hypophysitis with a dedicated section at the end for the hypophysitis secondary to CTLA-4 blockade.