Solitary extramedullary plasmacytoma in the larynx of a domestic cat.

Extramedullary plasmacytomas (EMPs) are uncommon neoplasms that rarely involve the feline larynx. This report details a solitary laryngeal EMP in a 12-year-old female domestic shorthair cat presenting with progressive dysphonia, dyspnea, and severe upper airway obstruction. Clinical and imaging examination revealed a mass originating from the epiglottis, causing severe chronic laryngeal stenosis. Due to the complexity and poor prognosis of the condition, euthanasia was elected. Histopathology demonstrated a non-encapsulated, submucosal proliferation of well-differentiated plasma cells within the epiglottis. The neoplastic cells exhibited mild to moderate cellular pleomorphism, characterized by anisocytosis, anisokaryosis, karyomegaly, occasional binucleation, and the presence of Mott cells. Immunohistochemistry (IHC) showed diffuse nuclear and cytoplasmic immunolabelling for MUM-1, confirming the plasma cell lineage. Based on the morphological and immunohistochemical findings, a diagnosis of solitary benign laryngeal EMP was established. This case emphasizes that while laryngeal EMPs are often histologically benign, their critical anatomical location can confer the potential for life-threatening obstructive respiratory disease. EMPs should thus be considered a key differential diagnosis for obstructive upper airway lesions in cats.