Immunohistochemical study for IgG4-positive plasmacytes in pituitary inflammatory lesions

On histology, IgG4-related hypophysitis is essentially similar to lymphocytic hypophysitis besides massive IgG4-positive plasmacyte infiltration. This immunohistochemical study was performed to investigate the presence of IgG4-positive plasmacytes in 14 various inflammatory lesions. Five cases of lymphocytic hypophysitis and a case of granulomatous hypophysitis were either negative or showed only a few IgG4-postive cells. A case of hypophysitis associated with pachymeningitis and a case of pituitary invasion of lymphoma were IgG4 negative. On the other hand, some IgG4-positive cells that tended to accumulate were observed in every six cases of secondary inflammation. In conclusion, immunohistochemistry for IgG4 can be a clue for differentiating IgG4-related hypophysitis from lymphocytic hypophysitis. However, clusters of IgG4-positive plasmacytes could be observed in secondary inflammation. Diagnosing hypophysitis with small biopsy specimen still remains troublesome.