#00065253

A 52-year-old male with a past medical history of diverticulitis presented with a one-month history of worsening abdominal and back pain, and an inability to walk due to the pain. Laboratory investigations revealed a positive COVID-19 test. His complete blood count showed hemoglobin (Hb) at 10.2 g/dl (reference range: 14.0-17.4 g/dl), mean corpuscular volume (MCV) at 79.7 fl (reference range: 80.0-96.0 fl), white blood cell (WBC) = 10.2 (4.8-10.8 k/ul) and platelets= 434 (150-400k/ul). Preoperative flexible sigmoidoscopy revealed foreign bodies in the sigmoid colon causing obstruction. He underwent sigmoid resection with an uncomplicated postoperative period. The peripheral smear showed a few plasmacytoid lymphocytes, rare plasma cells, and a single Mott cell, which is a rare plasma cell variant characterized by cytoplasm filled with Russell bodies. Typically, plasma cells produce immunoglobulins as part of the body's immune response, but overproduction and defective secretion can cause these proteins to accumulate in the endoplasmic reticulum and Golgi complex, forming Russell bodies. Under microscopic staining, Russell bodies appear eosinophilic but can dissolve during the staining process, leaving clear vacuoles within the cell. A plasma cell containing these immunoglobins is known as a Mott cell. Mott cells are rarely seen in peripheral blood. They are associated with plasma cell disorders such as multiple myeloma, chronic inflammation and autoimmune diseases. Recently, the presence of Mott cells has also been observed in COVID-19 patients (1,2), which is likely the case here.

Reference:

1.    Foldes D, Hinton R, Arami S, Bain BJ. Plasmacytoid lymphocytes in SARS-CoV-2 infection (Covid-19). Am J Hematol. 2020;95(7):861-862. doi:10.1002/ajh.25834

2.    Lüke F, Orsó E, Kirsten J, et al. Coronavirus disease 2019 induces multi-lineage, morphologic changes in peripheral blood cells. EJHaem. 2020;1(1):376-383. Published 2020 Jun 29. doi:10.1002/jha2.44