Thoracic and abdominal diagnostic imaging findings in dogs diagnosed with immune-mediated polyarthritis: 71 cases (2011-2023).

Objectives: To describe thoracic and abdominal imaging findings in dogs with immune-mediated polyarthritis and to evaluate their impact on the decision to commence immunosuppressive therapy.

Materials and methods: Retrospective case series describing imaging findings in dogs with immune-mediated polyarthritis across modalities, including thoracic radiographs, abdominal ultrasound, computed tomography, and where available, echocardiography. Additionally, two internal medicine clinicians reviewed the signalment, clinical signs, clinicopathological findings and diagnostic imaging results on two separate occasions, reaching a consensus for each dog on whether immunosuppression would be their treatment of choice or whether their recommendations would be altered by the results of diagnostic imaging.

Results: Seventy-one dogs met the inclusion criteria. Abnormal diagnostic imaging findings were identified in 25.4% (18/71) of dogs. Thoracic radiography did not identify significant imaging findings in any of the dogs. Lymphadenomegaly was the most commonly reported finding on computed tomography (32/40) and abdominal ultrasound (13/34). Neoplasia was identified in three dogs (3/71). Four (4/13) dogs had echocardiography findings consistent with endocarditis. Immunosuppression without performing diagnostic imaging would have been considered in 41 of 71 (57.7%) dogs, based on the signalment, presenting signs, results of physical examination and clinicopathological testing. Of these, 10 dogs (24.3%) had diagnostic imaging findings suggestive of an underlying trigger, therefore changing the clinician's decision to proceed with immunosuppression.

Clinical significance: Abdominal imaging and echocardiography should be prioritised over thoracic radiography, in dogs with immune-mediated polyarthritis. Signalment, presenting complaint, physical examination findings and clinicopathological results are not reliable predictors of abnormal diagnostic imaging findings in dogs with immune-mediated polyarthritis.