Joint‐Specific Memory and Sustained Risk for New Joint Accumulation in Autoimmune Arthritis

ObjectiveInflammatory arthritides exhibit hallmark patterns of affected and spared joints, but in each individual, arthritis affects only a subset of all possible sites. The purpose of this study was to identify patient‐specific patterns of joint flare to distinguish local from systemic drivers of disease chronicity.MethodsPatients with juvenile idiopathic arthritis followed without interruption from disease onset into adulthood were identified across 2 large academic centers. Joints inflamed at each visit were established by medical record review. Flare was defined as physician‐confirmed joint inflammation following documented inactive disease.ResultsAmong 222 adults with JIA, 95 had complete serial joint examinations dating from disease onset in childhood. Mean follow‐up was 12.5 years (interquartile range 7.9–16.7 years). Ninety (95%) of 95 patients achieved inactive disease, after which 81% (73 patients) experienced at least 1 flare. Among 940 joints affected in 253 flares, 74% had been involved previously. In flares affecting easily observed large joint pairs where only 1 side had been involved before (n = 53), the original joint was affected in 83% and the contralateral joint in 17% (P < 0.0001 versus random laterality). However, disease extended to at least 1 new joint in ~40% of flares, a risk that remained stable even decades after disease onset, and was greatest in flares that occurred while patients were not receiving medication (54% versus 36% of flares occurring with therapy; odds ratio 2.09, P = 0.015).ConclusionArthritis flares preferentially affect previously inflamed joints but carry an ongoing risk of disease extension. These findings confirm joint‐specific memory and suggest that prevention of new joint accumulation should be an important target for arthritis therapy.