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* Context. - Immunoglobulin G4 (IgG4)--related disease is a recently described entity that presents as mass-forming lesions in soft tissue, exocrine glands, and in lymph nodes as IgG4-related lymphadenopathy. The underlying patho- logic mechanism of IgG4-related disease is unclear; however, rituximab (an anti-CD20 monoclonal antibody) has been shown to have clinical efficacy.
Objective.-To look for the presence or absence of CD20 on the IgG4-expressing plasma cells in IgG4-related lymphadenopathy.
Design.-Twelve flow cytometry cases were identified through a retrospective review from the authors' institu- tions files. Cases were selected by the presence of a lymph node biopsy specimen with increased IgG4 plasma cells by immunohistochemistry and a histologic diagnosis compat- ible with IgG4-related lymphadenopathy.
Results.-We report dim CD20 expression on plasma cells in all cases for which a plasma cell population was clearly identified by flow cytometry. These cases were from patients with lymph node biopsy specimens that met published criteria for IgG4-related lymphadenopathy.
Conclusions.-This finding may be one potential expla- nation for the clinical efficacy of rituximab in IgG4-related disease.
(Arch Pathol Lab Med. 2013;137:1282--1285; doi: 10.5858/arpa.2012-0466-OA)
Immunoglobulin G4 (IgG4)--related disease (IgG4-RD) is name given to a recently described disorder that presents in soft tissues, often exocrine glands, as mass- forming lesions and in lymph nodes as IgG4-related lymphadenopathy (IgG4-RL). Plasma cells are polyclonal and predominantly of the IgG4 subtype, the rarest class of immunoglobulin. Diagnosis and recognition of this entity are critical to patient care, as many patients will present with multiple sites of involvement at different times.
Although initially recognized in the pancreas, and designated type 1 autoimmune pancreatitis, related lesions containing increased numbers of IgG4 plasma cells were subsequently identified throughout the body.1--3 A presumed autoimmune nature was attributed to affected patients because they frequently had autoantibodies (anti-dsDNA antibody, antinuclear antibody, and autoantibodies of an undetermined type).1--3 Currently, reported sites of involve- ment and disease associations are diverse and include central nervous system (pituitary gland, pachymeningitis), lacrimal gland (Mikulicz disease), ocular adnexa, sclerosing sialadenitis (Kuttner tumor), thyroid gland, pulmonary lesions, breast tissue, liver, idiopathic retroperitoneal fibro- sis, type 1 autoimmune pancreatitis, inflammatory aortic aneurysm, kidney, skin, and lymph node.1,3,4 The recurring nature of this disease, combined with the diversity of possible sites of involvement, can mean multiple resections and potential loss...