The prevalence of IgG4-positive plasma cells in hypophysitis: a possible relationship to IgG4-related disease.

Aims: Hypophysitis is a rare chronic inflammation of the pituitary gland corresponding currently to six histopathological subtypes. Among them, immuno-globulin-G4-related hypophysitis was recently added in this classification. The aim of this study was to perform a retrospective histopathological and immunohistochemical analysis to evaluate the prevalence of IgG4-related hypophysitis and review reported cases. Methods: All samples of hypophysitis from Lariboisiere hospital were reviewed by two pathologists to assess their subtypes. An immunohistochemistry against IgG4 and IgG was performed. Slides were numerized, and IgG4-positive plasma cells and IgG plasma cells were counted in three high-power fields to evaluate the ratio. Results: Eight cases were included: 5 lymphocytic hypophysitis, 1 granulomatous subtype, and 2 IgG4-related hypophysitis, affecting two young women without other coaffected organ. Conclusion: Our results show that IgG4-related hypophysitis is not an exceptional entity. Storiform fibrosis and obliterative phlebitis, histopathological characteristics of IgG4-related disease in other organs, are lacking in pituitary lesions. This study proves the interest of immunohistochemistry for diagnosis of IgG4-related hypophysitis. Due to the sensibility of IgG4-disease to steroids in other organs, this finding could be of clinical relevance.