Pituitary metastasis of breast cancer mimicking IgG4-related hypophysitis

IgG4-related hypophysitis, which is the pituitary gland inflammation caused by IgG4 positive lymphocytes, can affect cavernous sinus and orbital apex leading to developing cranial nerve related symptoms such as orbital apex syndrome (OAS). Here we report a case of hypopituitarism associated with OAS caused by pituitary metastasis of the breast cancer with elevated serum IgG4 level, who initially resembled to IgG4-related hypophysitis. Although this case had some features in common with igG4-related hypophysitis. The symptoms and pituitary enlargement were typical. However, steroid treatment did not improve her symptoms. Thus, we performed a tissue biopsy. Histopathologic examination of the hypophyseal tumor confirmed metastatic breast cancer in her pituitary. Pituitary metastatic tumor should be suspected if a case with OAS was once diagnosed as a cancer.