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

Hypophysitis is a rare chronic inflammation of the pituitary gland corresponding currently to six histopathological subtypes. Among them, immunoglobulin- 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.

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.

Eight cases were included: 5 lymphocytic hypophysitis, 1 granulomatous subtype, and 2 IgG4-related hypophysitis, affecting two young women without other coaffected organ.

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.