plasmacytosis plasmacytosis plasmacytosis is a condition in which there is an unusually large proportion of plasma cells in tissues, exudates, or blood.: 743 plasmacytosis may be divided into two types—cutaneous and systemic—both of which have identical skin findings.: 743 patients with plasmacytosis have been predominantly found to have lung infections (pneumonia, tuberculosis, abscess) whereas multiple myeloma is rarely found. this article is about the disease found in humans. for the disease that affects mustelids, see aleutian disease. plasmacytosis