Unusual IgG4-related hypophysitis: one case report and analysis of clinicopathological characteristics

Abstract

Background Immunoglobulin G4 (IgG4)-related disease is a recently characterized autoimmune disease entity marked by elevated serum IgG4 levels and tissue infiltration by IgG4-positive plasma cells in multiple involved organs. Hypophysitis is a rare inflammatory disorder and IgG4-related sclerosing disease involving the ituitary alone is especially rare. Imaging studies may reveal a mass lesion in the sellar area or a thickening of pituitary stalk, mimicking a pituitary tumor. Due to its rarity and non-specific appearance in radiological examination, it is a diagnostic challenge for clinicians and histopathologists to differentiate solitary IgG4-related hypophysitis from other pituitary lesions. The aim of this study is to summarize the clinicopathological features of unusual IgG4-related hypophysitis and discuss the differential diagnosis of histologically similar inflammatory lesions in pituitary. Methods The clinical manifestation of a patient with solitary IgG4-related hypophysitis was presented retrospectively. Resected mass was routinely paraffin-embedded and stained with Hematoxylin and Eosin. Dako EnVision immunohistochemical staining system was used to detect the tumor antigen expressions, including vimentin (Vim), S-100 protein (S-100), pan cytokeratin (PCK), epithelial membrane antigen (EMA), CD3, CD20, CD68, CD1a, κ-light chain, λ-light chain and progestrone receptor (PR).  Results A 47-year-old male patient presented with 1-year history of mild limb weakness and hyposexuality. Laboratory examination revealed hypopituitarism with low levels of serum testosterone, cortisol, luteinizing hormone (LH) and follicle stimulating hormone (FSH), although his serum IgG4 level was high. MRI of the pituitary gland revealed a mass lesion in the sellar area with T₁WI mild hyperintense and homogeneous enhancement after gadolinium administration. The patient underwent a transsphenoidal mass resection of the pituitary gland. Histological examination showed bland appearing spindle cell proliferation in the sclerotic background with marked infiltration of lymphocytes, plasma cells, as well as multiple foci of meningothelial-like nodules at the periphery of tissues. Immunohistochemical staining showed that the lymphocytes were positive for CD3 and CD20. Plasma cells were distinct and the number of κ and λ-light chains was the same. There were more than 30 IgG4-positive plasma cells per high power field (HPF), which accounted for greater than 40% of the IgG-positive plasma cells. The meningothelial-like nodules were positive for Vim, EMA and PR, but negative for CD68, S-100 and CD1a. A final histological diagnosis of IgG4-related hypophysitis with meningothelial reaction was made. The patient took prednisolone orally at 35 mg/d for 2 weeks, and the symptoms of limb weakness and hyposexuality showed improvement. The mass lesion of pituitary gland demonstrated a reduction in size. The prednisolone therapy was continued at a dose of 30 mg/d to prevent recurrence of IgG4-related disease.  Conclusions IgG4-related hypophysitis is a rare disease of central nervous system with good response to corticosteroid treatment. Due to the relative paucity of reported cases and similarities in histological findings, it may be difficult to differentiate IgG4-related disease from other pituitary lesions with prominent inflammatory cell infiltration and stromal fibrosis. Thorough inspection under the microscopy and more importantly elevated serum IgG4 level are necessary for correct diagnosis.

doi: 10.3969/j.issn.1672-6731.2014.10.012