History
A 3-year-old 40.5-kg (89.1-lb) castrated male Labrador Retriever–mixed breed dog was admitted to the University of Illinois Veterinary Teaching Hospital because of a 10-day history of stridor and inspiratory obstructive dyspnea. The clinical signs were intermittent and paroxysmal (5 minutes’ duration/episode) and sometimes related to exercise.
Clinical and Gross Findings
At admission, findings of a physical examination, CBC, serum biochemical profile, urinalysis, and coagulation profile were unremarkable. The dog was breathing normally in the examination room. Tracheal radiography identified an intratracheal circular 1.7-cm-diameter soft tissue mass at the level of the fourth and fifth cervical vertebrae. The mass occupied 80% of the internal diameter of the trachea on the lateral view. Tracheoscopy revealed a rounded, mildly irregular, and pedunculated mass extending from the dorsal tracheal membrane (Figure 1) at approximately 35 cm from the tip of the nose. The mass was obstructing approximately 90% of the tracheal lumen. No other lesions were found caudally. The mass was removed by tracheal resection and anastomosis and submitted to the University of Illinois Veterinary Diagnostic Laboratory for diagnostic examination.
Tracheoscopic image of a tracheal mass in a 3-year old dog with a history of intermittent and paroxysmal episodes of stridor and inspiratory obstructive dyspnea during the preceding 10 days. Notice the smooth and pedunculated aspect of the mass extending from the dorsal tracheal membrane. The mass was estimated to be obstructing approximately 90% of the tracheal lumen.
Citation: Journal of the American Veterinary Medical Association 250, 9; 10.2460/javma.250.9.993
Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→
Histopathologic Findings
Histologic evaluation of the excised intraluminal mass revealed a neoplastic population of round cells tightly packed in a thin fibrovascular stroma (Figure 2). The cytoplasm of the cells was eosinophilic and granular, and contained a pale paranuclear halo (Golgi zone). Nuclei were round and eccentrically located, with finely stippled chromatin. Frequent giant bi- or multinucleated cells (as many as 6/hpf [40X objective]) were observed. Anisocytosis and anisokaryosis were moderate, and the mean number of mitotic figures per 10 hpf was 3. Neoplastic tissue did not extend to the margins of the resected mass. Immunohistochemical analysis revealed that the neoplastic cells were negative for chromogranin A (a neuroendocrine marker) and positive for multiple myeloma oncogene 1 (MUM1; a plasma cell marker). Immunohistochemical staining for MUM1 had a nuclear location and was of moderate to high intensity; MUM1 expression was evident in approximately 75% of the cells, including the multinucleated cells.
Photomicrographs of sections of the tracheal mass excised from the dog in Figure 1. A—Notice the neoplastic population of round cells tightly packed in a thin fbrovascular stroma. H&E stain; bar = 50 μm. B—The neoplastic cells are positive for multiple myeloma oncogene 1 (MUM1 [brown staining]). MUM1-specific immunohistochemical reaction; bar = 50 μm.
Citation: Journal of the American Veterinary Medical Association 250, 9; 10.2460/javma.250.9.993
Morphologic Diagnosis and Case Summary
Morphologic diagnosis and case summary: tracheal plasmacytoma in a 3-year-old dog.
Comments
The case described in the present report involved a young dog with a tracheal plasmacytoma. Canine primary tracheal tumors are often associated with a bimodal age distribution; osteochondroma, ecchondroma, and chondrosarcoma develop in younger dogs, whereas other tumor types develop in dogs > 6 years of age.1 Plasmacytomas are an extremely rare type of tracheal neoplasm in dogs; to our knowledge, there are only 5 reported cases2–6 in the veterinary medical literature, and all of those dogs were > 6 years of age. Among those 5 case reports, 4 had a thorough morphologic and histologic description of the tumor.2–5 As in the dog of the present report, the previously described tumors were pedunculated masses arising from the dorsal tracheal membrane.2–5 Osteochondromas and ecchondromas originate not from the dorsal tracheal membrane but from the cartilaginous rings7; therefore, these tumor types were not considered differential diagnoses in this case. Four of the 5 previously described tracheal plasmacytomas developed in male dogs, which might suggest a sex predisposition.3–6 These features regarding tumor origin and sex of an affected dog might increase the index of suspicion for tracheal plasmacytoma, even in young individuals.
For the dog of the present report, a histologic diagnosis of plasmacytoma was confirmed on the basis of immunohistochemical analysis for MUM1. Multiple myeloma oncogene 1, also called interferon regulatory factor-4, is involved in lymphoid cell differentiation.8 It is required for immunoglobulin light-chain rearrangement at the pre-B stage of lymphocyte maturation.9 Immunohistochemical staining for MUM1 has been shown to have high sensitivity (93.5%) and specificity (92.1%) for diagnosis of plasmacytomas in dogs.10 Ideally, bone marrow aspirate specimens should have been collected for cytologic evaluation to definitively exclude multiple myeloma11 in the dog of the present report. However, a diagnosis of multiple myeloma was unlikely given the absence of notable abnormalities revealed by physical examination, routine blood analyses, and urinalysis; the absence of radiographic lytic bone lesions; and the similarity of findings to previously reported gross and histologic descriptions of tracheal plasmacytoma.
For dogs, prognosis associated with tracheal plasmacytoma seems to be favorable, with surgical excision being curative for 4 of the 5 previously described cases.2–4,6 The dog in the present report underwent a CT examination 9 months after surgery. No tumor regrowth was observed at that time, and the owner had not noticed any respiratory tract signs since surgery.
References
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2. Chaffin K, Cross AR, Allen SW, et al. Extramedullary plasmacytoma in the trachea of a dog. J Am Vet Med Assoc 1998; 212: 1579–1581.
3. Palacios D, Font A, Closa JM, et al. Intratracheal plasmacytoma in a dog: diagnosis and treatment. Clin Vet Pequenos Anim 2010; 30: 25–29.
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11. Vail DM. Plasma cell neoplasms. In: Withrow SJ, Vail DM, eds. Withrow and MacEwen's small animal clinical oncology. 4th ed. Philadelphia: WB Saunders Co, 2007; 769–784.
