Extramedullary laryngeal plasmacytoma in a dog

CASE HISTORY: An 8-year-old, female, spayed Border Collie presented with a 3-week history of coughing, choking and haemoptysis. CLINICAL FINDINGS: Inspiratory stridor was evident on clinical examination. Cervical radiographs revealed a round soft-tissue mass on the dorsal aspect of the epiglottis. A laryngeal mass was evident on examination under anaesthesia, and an incisional biopsy was obtained. Histopathology revealed a dense proliferation of neoplastic round cells morphologically consistent with plasma cell origin. Immunohistochemisty results were negative for CD3 (T cell marker) and positive for CD79a (B cell marker), resulting in a diagnosis of extramedullary plasmacytoma. The patient was treated with melphalan and prednisolone; clinical signs resolved within 1 week and the mass was no longer evident on laryngoscopy after 1 month of treatment. After 6 months of chemotherapy, the laryngeal mass recurred and euthanasia was requested. There was no evidence of systemic spread on post-mortem examination. DIAGNOSIS: Solitary extramedullary plasmacytoma of the canine larynx. CLINICAL RELEVANCE: Respiratory extramedullary plasmacytomas are extremely rare with only one laryngeal and two tracheal cases previously reported. This is the first published report of a laryngeal plasmacytoma that recurred despite combination chemotherapy with melphalan and prednisolone.