Sinonasal plasmacytoma in a cat.

A 13-year-old female spayed Domestic Shorthair cat presented with a history of right-sided mucopurulent nasal discharge for 18 months. Computed tomography revealed a mass within the right nasal cavity and the right frontal sinus. The animal was euthanized, and a postmortem examination was performed. On macroscopic examination, the right nasal cavity and the right frontal sinus were partially occluded by a soft whitish mass. Microscopically, the mass was composed of well-differentiated plasma cells that were immunopositive for immunoglobulin G and lambda light chains. These findings were consistent with a mature-type sinonasal plasmacytoma. In addition, there was right-sided mucopurulent rhinitis and sinusitis caused by a Pasteurella infection, which probably developed secondary to the sinonasal plasmacytoma. To the authors' knowledge, this is the first report of a sinonasal plasmacytoma in a cat. The present communication shows that feline sinonasal plasmacytomas should be included in the differential diagnosis for tumors located in the upper respiratory tract of cats.