Paraneoplastic T cell lymphocytosis associated with a thymoma in a dog

Abstract

A four-year-old male neutered Australian shepherd dog was diagnosed with a thymoma and concurrent mature T cell lymphocytosis. The lymphocytosis consisted of a mixed population of T cells expressing either CD4 or CD8 or neither marker, and the result of polymerase chain reaction for antigen receptor rearrangement was negative. The peripheral lymphocytosis resolved within 24 hours following thoracotomy and thymectomy. Similar cases have been reported in man, but the aetiology of the increased circulating lymphocytes remains unclear. Although peripheral lymphocytosis is an uncommon paraneoplastic syndrome associated with thymomas, thymoma should be considered as a differential when the increased lymphocytes consist of a mixed population of T cells.

Thymoma related myasthenia gravis in humans and potential animal models

“…respiratory distress or pain) [104,114], and rare blood lymphocytosis both responding to thymoma removal have been observed in thymoma-bearing animals as in humans [115]. By contrast, autoimmune phenomena are rare (see below).…”

Perioperative Mortality and Long‐Term Survival in 80 Dogs and 32 Cats Undergoing Excision of Thymic Epithelial Tumors

“…[9][10][11][12] Clinical signs may also result from paraneoplastic syndromes including myasthenia gravis 11,[13][14][15][16][17][18][19][20][21][22][23] or polymyositis in dogs and cats, 19,24 hypercalcemia in dogs, 11,13,25,26 and exfoliative dermatitis in cats. 24,[27][28][29][30][31] Concurrent non-thymic cancers 11,18 and T-cell lymphocytosis 32 have also been reported in dogs. Distant metastasis is uncommon in both species.…”

Marked cytoreduction of a lymphocyte-rich mediastinal thymoma with neoadjuvant chemotherapy in a cat

“…Given the subsequent resolution of the lymphocytosis and the subsequent diagnosis of a non-lymphoproliferative neoplasm, additional diagnostic tests such as flow cytometry and PARR assay were not pursued to further characterise this population; and given the small and well-differentiated nature of these cells a reactive process was favoured. Interestingly, peripheral T-cell lymphocytosis has been reported in association with lymphocyte rich-thymomas in humans and one dog, 23,24 and it is possible that the peripheral lymphocytosis in this case may have been reflective of a similar paraneoplastic syndrome.…”