Inflammatory back pain (IBP) is often an early manifestation of spondyloarthritis (SpA), but the prognosis of patients with incident IBP is unknown. This study was undertaken to investigate long-term outcomes in patients with IBP, and predictors of progression to SpA, in a population-based cohort.
We conducted a retrospective, longitudinal study using the Rochester Epidemiology Project, a longstanding population-based cohort of residents of Olmsted County, MN. Patients ages 16-35 years with clinical visits for back pain from 1999 to 2003 were identified, and we screened these patients for the presence of new-onset IBP and performed medical record reviews to collect data on clinical, laboratory, and imaging features of SpA. Outcomes in these patients were followed up until July 2016. We used survival analysis for competing risks to examine progression to either SpA, a non-SpA diagnosis, or resolution of back pain. Recursive partitioning was used to identify predictors of progression to SpA.
Among 5,304 patients with back pain, we identified 124 patients with new-onset IBP. After a median follow-up of 13.2 years, IBP had progressed to SpA in 39 patients, 15 patients developed a non-SpA diagnosis, and 58 patients had resolution of IBP. At 10 years, the probability of having SpA was 30%, while the probability of resolution of IBP was 43%. The most important predictors for progression to SpA were uveitis, male sex, and family history of SpA.
In a minority of patients, new-onset IBP progresses to SpA, while IBP resolves in many. That IBP often resolves may explain the difference between the prevalence of IBP (3-6%) and the prevalence of SpA (0.4-1.3%).