Nodal involvement of extranodal marginal zone lymphoma with extreme plasmacytic differentiation (Mott cell formation) simulating plasma cell neoplasm and lymphoplasmacytic lymphoma

which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Nodal involvement of extranodal marginal zone lymphoma with extreme plasmacytic differentiation (Mott cell formation) simulating plasma cell neoplasm and lymphoplasmacytic lymphoma TO THE EDITOR: Plasmacytic differentiation is not a rare feature of extranodal marginal zone lymphoma of muco-sa-associated lymphoid tissue (MALT lymphoma), and serum paraproteinemia is detected in more than a third of patients, suggesting that at some point, the distinction from plasma cell neoplasm (PCN) is ambiguous [1, 2]. Moreover, the endoscopic findings may be very subtle in the early stages and appear slightly nodular or atrophic, indicating the lack of a consistently clear morphologic distinction from chronic gastritis [2, 3]. A focus on a predominantly nodal presentation, serum monoclonal gammopathy, and plasma-cytoid histology can lead to a wrong diagnosis such as PCN or lymphoplasmacytic lymphoma (LPL), especially when Mott cells, the characteristic hypersecretory plasma cells, are predominant in a small lymph node biopsy. Recently, we encountered the first such case in a generally healthy elderly man who was initially diagnosed with PCN or LPL. This 72-year-old man with no specific symptoms presented with a mass-like lesion on the tail of the pancreas, incidentally detected on ultrasonography during a routine health examination (Fig. 1A). The patient's serum lactate dehydrogenase and creatine phosphokinase levels were elevated at 728 IU/L and 395 U/L, respectively, although the level of carbohydrate antigen 19-9, a pancreatic carcinoma marker, was within the normal range (16 U/mL). Subsequent computed tomography (CT) imaging revealed that the mass-like lesion was actually not a pancreatic mass but rather conglomerated, enlarged lymph nodes (4 cm in total) around the pancreas (Fig. 1B). In addition, multiple paraaortic and abdominal lymph nodes were enlarged, which suggested disseminated nodal lymphoma. A percutaneous core needle biopsy was obtained from an enlarged lymph node near the stomach. Upon microscopic examination, a diffuse proliferation of monotonous small atypical lymphocytes and striking infiltration of hypersecretory plasma cells with eosinophilic intracytoplasmic immunoglobulin globules (Russell bodies), the so-called " Mott cells " or " grape-like cells " (Fig. 2A), were observed. As Mott cells are often considered a good diagnostic indicator of lymphoma with pathologically distinct plasmacytic differentiation, the possibility of PCN or LPL was suspected. Subsequent serum immunoglobulin quantifi-cation also revealed kappa light chain restriction (20.30 mg/L). Gastroduodenoscopy and colonoscopy were performed concurrently to evaluate a possible primary lesion in …