Extramedullary conjunctival plasmacytoma in a cat

Purpose: To describe a case of solitary conjunctival plasmacytoma in a cat. Methods: A 9 year-old female Domestic shorthaired cat was referred with a 3 weeks history of protrusion of the left third eyelid. Results: Ophthalmic examination showed conjunctival hyperemia and a smooth nodule on the bulbar aspect of the third eyelid. Globe retropulsion was normal. Cytologic smears of the mass revealed sheets of round cells with eccentric nucleus, characteristic cartwheel appearance, and abundant cytoplasm with clear perinuclear halo, highly suggestive of plasmacytoma. Accurate stadiation was performed excluding clinical signs of multiple myeloma. The third eyelid was excised and submitted for histology. Histologically, a poorly defined neoplastic mass, 1.5 cm in diameter, expanded nictitans conjunctiva substituting lacrimal gland. The mass was composed of dense sheets of round cells morphologically consistent with mature plasma cells. Anisocytosis and anisokaryosis were mild and rare binucleated giant cells were observed. Mitoses were rare. Neoplastic cells were immunohistochemically positive for CD20 and lambda chains and negative for CD3. Based on histological, immunophenotypical and clinical findings a diagnosis of extramedullary plasmacytoma of the third eyelid was posed. No recurrence has been noted 5 months after surgery. Conclusions: Conjunctival solitary extramedullary plasmacytoma is a rare tumor in human beings. In the feline species, intraocular and orbital but not conjunctival solitary plasmacytomas have been reported so far. Since in the cat, in contrast to human, well differentiated myeloma commonly have extramedullary involvement, in the diagnosis of solitary plasmacytoma it is important to rule out a myeloma-related disorder.