#00065968

A 64-year-old woman presented with IgG lambda monoclonal gammopathy, with otherwise normal CBC and CMP results and no lytic lesions on imaging. Bone marrow biopsy revealed a normocellular marrow infiltrated by abnormal plasma cells with prominent cytoplasmic vacuolization forming Russell bodies (panels A [×200] and B [×1000], H&E). The plasma cells expressed CD138 and MUM1 (panel C and inset, respectively, ×200) and showed lambda light chain restriction by in-situ hybridization (panels D [lambda] and E [kappa], ×400). Russell bodies were also noted on aspirate smears (panel F, ×1000). 

Prominent Russell bodies are a distinctive but uncommon morphological feature. Russell bodies represent immunoglobulin accumulations within the rough endoplasmic reticulum, forming large eosinophilic inclusions. Their presence reflects excessive immunoglobulin production or impaired secretion and can occur in both reactive and neoplastic plasma cell conditions.