Presumptive Post-Chemotherapy Polyarthritis in a Maltese Dog: Clinical Characteristics and Outcome

Resumo

Background: Post-chemotherapy polyarthritis is a recognized chemotherapy-related complication in human oncology but has not been clearly documented in dogs. Non-septic arthritis has been mentioned only once as an adverse effect of chemotherapy in dogs without detailed clinical features. In human medicine, post-chemotherapy polyarthritis has been reported across multiple chemotherapy protocols including doxorubicin. This report describes the 1^st presumptive case of doxorubicin-associated non-septic inflammatory polyarthritis in a dog, suggesting a possible parallel to post-chemotherapy polyarthritis reported in human cancer patients.

Case: An 11-year-old spayed bitch Maltese presented with lethargy, hyporexia, and lameness 4 months after initiating an adjuvant chemotherapy with doxorubicin administered following unilateral nephrectomy for renal hemangiosarcoma. Physical examination revealed pyrexia, weight loss and swelling with warmth of the right hock joint. Hematologic evaluation identified moderate normocytic normochromic non-regenerative anemia, neutrophilia and monocytosis with marked elevation in C-reactive protein concentration. Diagnostic imaging including radiography, ultrasonography and computed tomography revealed no evidence of tumor recurrence or other sources of inflammation. Infectious disease testing, including polymerase chain reaction panels, yielded negative results. Arthrocentesis of multiple joints showed increased nucleated cell counts with neutrophilic inflammation and absence of infectious organisms. Synovial fluid culture, antinuclear antibody titers and rheumatoid factor tests were all negative. Non-infectious inflammatory polyarthritis was diagnosed and presumed to be secondary to chemotherapy based on clinical progression and exclusion of alternative causes. Treatment with prednisolone and mycophenolate mofetil resulted in complete remission and normalization of inflammatory markers. The patient remained clinically stable for 5 months after diagnosis, and died due to systemic metastasis of hemangiosarcoma confirmed on postmortem examination.

Discussion: This case describes the temporal association between chemotherapy and the onset of polyarthritis in a bitch, proposes a diagnostic approach for dogs based on diagnostic criteria reported in human patients, and suggests an immune-mediated mechanism consistent with this condition. Although the mechanism of post-chemotherapy polyarthritis has not been fully understood, immune dysregulation after chemotherapy has been consistently suggested as a potential cause. In human medicine, joint manifestations typically arise 2 to 8 months after the initiation of chemotherapy, which aligns with the onset observed in this bitch. Diagnostic considerations for this condition in human studies include a confirmed diagnosis of cancer, documented exposure to chemotherapy, development of joint disease without previous joint disorder and no other identifiable cause of arthritis. The clinical features in this patient fulfilled these criteria, strengthening the suspicion that chemotherapy contributed to joint disease development. Therapeutic strategies reported in human patients generally rely on immunomodulatory treatment. In this case, prednisolone and mycophenolate mofetil were selected, resulting in complete resolution and sustained clinical stability. This favorable response supports the immune-mediated process and suggests that immunosuppressive therapy may be effective for managing post-chemotherapy polyarthritis in dogs. This case provides a detailed description of clinical presentation and progression of presumptive post-chemotherapy polyarthritis in a dog. Recognition of this potential chemotherapy-associated complication is essential, and rigorous patient monitoring after initiation of chemotherapy is warranted.

Keywords: chemotherapy, dog, immunosuppressant, lameness, post-chemotherapy polyarthritis.