Ultrasound microvascular flow imaging and photon counting computed tomography support the diagnosis and assist in treatment monitoring of canine erosive immune mediated polyarthropathy: a case report.

Introduction: Erosive immune-mediated polyarthritis (IMPA) carries a poor prognosis due to irreversible joint destruction and poor response to therapy. Monitoring response to therapy can be challenging as systemic markers like C-reactive protein (CRP) are nonspecific for underlying causes of inflammation and repeated joint fluid collection by arthrocentesis for cytological analysis is invasive. In humans, several imaging methods are used to monitor synovial or periarticular blood flow including diagnostic ultrasound with advanced microvascular imaging (MVI) or power Doppler (PD) and spectral CT techniques like iodine overlay-mapping with photon counting computed tomography (PCCT). These noninvasive methods are used to detect and describe vascular flow reflective of synovitis in IMPA. PCCT may also provide more sensitive means of detecting minute erosive changes, compared to traditional CT and radiographs. Methods: A retrospective clinical case study was conducted on a 6-year-old, intact female Yorkshire Terrier suffering from erosive IMPA that was previously systemically healthy. Traditional examination and diagnostics, including radiography, baseline blood work, tick borne disease testing, urinalysis, joint fluid cytology, and CRP supported but did not confirm erosive IMPA. Further imaging was conducted, consisting of dorsal carpal B-mode ultrasound, ultrasound with PD and MVI, and PCCT with iodine contrast. These novel imaging techniques were paired with joint fluid cytology and CRP and repeated 12 weeks after initiating immunosuppressive oral corticosteroid therapy. Results: Initial PCCT revealed an erosive arthropathy of the left carpus with secondary subluxation of the radiocarpal joint and questionable subchondral erosive changes to the right intermedioradial carpal bone. PCCT with iodine mapping and MVI showed marked left carpal and mild right carpal synovitis. PD did not demonstrate increased synovial vascular flow. After 12 weeks of prednisolone immunosuppression, significant reduction in synovitis without progression of erosive changes were noted on repeated imaging tests, coinciding with improvements in paired joint fluid cytology and C-reactive protein. Discussion: Ultrasound with MVI and PCCT helped achieve a diagnosis of erosive IMPA in a dog and effectively monitored response to treatment. Such novel advanced imaging has potential for broader impact regarding early detection, prognosis, treatment decision-making, and long-term monitoring for inflammatory canine joint disease.