Serum Biomarkers of Clinical and Cytologic Response in Dogs with Idiopathic Immune‐Mediated Polyarthropathy

BACKGROUND Immune-mediated polyarthopathy (IMPA) is common in dogs, and is monitored by serial arthrocenteses. HYPOTHESIS/OBJECTIVES Plasma C-reactive protein (CRP), interleukin-6 (IL-6), and CXCL8 (interleukin-8) would serve as noninvasive markers of joint inflammation in IMPA. ANIMALS Nine client-owned dogs with idiopathic IMPA; 6 healthy controls. METHODS Prospective study. Plasma CRP, IL-6, and CXCL8 were measured by ELISA at baseline, 2, and 4 weeks during treatment with prednisone at 50 mg/m(2) /day. Arthrocenteses, the canine brief pain inventory (CBPI), and accelerometry collars were used to assess joint inflammation, lameness, and mobility at all 3 time points. RESULTS C-reactive protein concentrations were higher in IMPA dogs (median 91.1 μg/mL, range 76.7-195.0) compared with controls (median <6.3 μg/mL, <6.3-13.7; P = .0035), and were significantly lower at week 2 (10.6 μg/mL, <6.3-48.8) and week 4 (<6.3 μg/mL, <6.3-24.4; P < .001). C-reactive protein was correlated with median CBPI scores (r = 0.68; P = .0004), joint cellularity (r = 0.49, P = .011), and mobility by accelerometry (r = -0.42, P = .048). Plasma IL-6 concentrations were also higher in IMPA dogs (median 45.9 pg/mL), compared with controls (median <15.7 pg/mL; P = .0008). IL-6 was lower in IMPA dogs by week 4 (<15.7 pg/mL; P = .0099), and was modestly correlated with CBPI scores (r = 0.47, P = .023). CXCL8 did not differ significantly between IMPA and healthy dogs. CONCLUSIONS Plasma CRP and IL-6 might be useful surrogate markers of synovial inflammation and disease activity in dogs with IMPA.