Extramedullary Intratracheal Plasmacytoma in a Bitch

Abstract

Background: Plasma cell tumors occur in 2 forms: multiple myeloma and solitary plasmacytoma. The latter can present as bone and/or extramedullary, which is the type most frequently diagnosed in the skin of dogs. In addition to the skin, organs of the respiratory, alimentary, and urinary tracts can be considered primary sites. When viewed macroscopically, extramedullary plasmacytomas are small, elevated, solitary, and single; and upon sectioning, well-delimited, non-encapsulated, white, and/or reddish. These tumors are also frequently associated with immunoglobulin production and amyloid deposition. Therefore, the objective of the present study is to report the case of an extramedullary plasmocytoma in the trachea of a bitch.

Case: A bitch mongrel of unknown age that presented with respiratory symptoms was diagnosed through radiological examination as having a tracheal foreign body occluding 75% of the lumen. However, during the surgical procedure of tracheotomy, a mass was found adhered to the tracheal mucosa. Surgical excision of the mass and adjacent tracheal rings was subsequently performed and the material was sent for histopathological examination. Macroscopic evaluation revealed the presence of a firm and whitish nodular structure with dimensions of 1.0 × 1.2 × 1.5 cm. Histological evaluation of the tissue showed highly cellular, well-defined, and expansive neoplastic proliferation of round cells, which extended from the submucosal layer towards the lumen. The cells were organized in well-grouped bundles and trabeculae on scarce fibrovascular stroma, which were predominantly rounded and with borders sometimes distinct, sometimes indistinct. The cytoplasm ranged from scarce to moderate, eosinophilic, and homogeneous, with central to paracentral rounded nuclei with dense chromatin and sometimes evident nucleoli. Moderate anisokaryosis and anisocytosis, with rare presence of binucleated cells and mitotic figures. Based on the aforementioned findings, the presumptive diagnosis was an undifferentiated round cell neoplasm. After a subsequent immunohistochemical evaluation with positive staining for MUM1, CD45RA, and lambda immunoglobulin light chain, a final diagnosis of solitary extramedullary plasmacytoma of the trachea was suggested.

Discussion: Although plasmacytoma is considered a common cutaneous neoplasm, reports are scarce in other tissues, especially in the trachea, as observed in the present case. In view of the anatomical location and expansive growth of this tumor, the clinical symptomatology presented by the patient were due to the reduction and difficulty in the passage of air through the upper airway. Plasmacytoid tumors are easily recognized by the very distinct morphological features of the plasma cells, which exhibit a whitish perinuclear halo (Golgi complex). Nonetheless, in cases where there is marked cellular pleomorphism, cells may lose their normal features, making the histological diagnosis complex and warranting complementary exams such as immunohistochemistry. The use of specific antibodies such as MUM-1, CD20, CD18, CD45RA, CD79α, or IRF4 help in the diagnostic procedure, as they are sensitive and specific for plasma cell neoplasms, so their use along with histopathology is essential for a more accurate diagnosis.

Keywords: dog, round cells, histopathology, immunohistochemistry.

Título: Plasmocitoma extramedular intratraqueal em uma cadela

Descritores: cão, células redondas, histopatologia, imuno-histoquímica.