Cytoplasmic inclusions in leukocytes: An unusual manifestation of cryoglobulinemia

Cryoglobulins are circulating immunoglobulins characterized by reversible, cold-induced precipitation. A variety of laboratory abnormalities, including hypocomplementemia, elevated erythrocyte sedimentation rate, rheumatoid factor activity, pseudoleukocytosis, and pseudothrombocytosis, are associated with cryoglobulinemia. Extracellular, faintly basophilic, amorphous deposits of cryoglobulins occasionally have been described in blood smears. In the present study, smears prepared from blood collected at room temperature from 6 patients with cryoglobulinemia exhibited neutrophil and, occasionally, monocyte inclusions containing clear, light pink, or faintly basophilic amorphous material. The inclusions were absent in smears from blood collected and maintained at 37°C. Ultrastructural examination revealed that the material within the leukocyte inclusions was consistent with phagocytosed immunoglobulins. The identification of characteristic cytoplasmic inclusions in leukocytes may be an important clue in the early recognition of cryoglobulinemia.