Mediastinal T-cell lymphoma with presumed secondary monostotic long bone involvement in the absence of local recurrence

A 7-year-old male neutered cocker crossbreed was presented with a 1-month history of tachypnoea and exercise intolerance. Initial investigations confirmed a pleural effusion due to a mediastinal T-cell lymphoma. L-asparaginase and a 23-week lomustine, vincristine, prednisolone protocol were pursued and complete response was recorded at the end of the protocol. Ten months later, he was presented at the referring veterinary practice with a non-bearing lameness of his left forelimb, and a transcondylar screw was placed following the suspicion of a fracture of the lateral humeral epicondyle. During surgery, a sample of bone was collected and submitted for histopathology. Histopathology and immunohistochemistry were consistent with a T-cell lymphoma. Total body CT scan revealed a monostotic aggressive lesion of the distal humerus with no evidence of infiltration into bone at any other sites, and no other signs of lymphoma relapse were seen elsewhere in the body. Based on these findings, secondary bone lymphoma was hypothesised.