Back pain and health status in patients with clinically diagnosed ankylosing spondylitis, psoriatic arthritis and other spondyloarthritis: a cross-sectional population-based study

Background: In the broader spectrum of back pain, inflammatory back pain (IBP) is a symptom that may indicate axial spondyloarthritis (SpA). The objectives of this study were to determine the frequency of current IBP, as a hallmark sign of possible axial SpA, in patients with ankylosing spondylitis (AS), psoriatic arthritis (PsA) and other SpA and to compare self-reported health between the groups with current IBP. Methods: Five-thousand seven hundred seventy one patients identified in the regional healthcare register of the most southern county of Sweden, diagnosed at least once by a physician (based on ICD-codes) with any type of SpA in 2003-2007, were sent a postal survey in 2009. Patients with current IBP were identified, based on self-reported back pain >= 3 months in the preceding year and fulfilling the Berlin criteria for IBP. The frequencies of IBP in AS, PsA and other SpA (including the remaining subgroups of SpA) were determined, and the groups were compared with regard to patient reported outcome measures (PROMs). Results: The frequency and proportion of patients with current IBP in AS, PsA and other SpA were 319 (43 %), 409 (31 %) and 282 (39 %) respectively, within the responders to the survey (N = 2785). The proportion was statistically higher in AS, compared to PsA (p < 0.001), but not for AS compared to other SpA (p = 0.112). PsA and other SpA, with current IBP, had similar (BASFI, EQ-5D, patients global assessment, fatigue, spinal pain) or worse (BASDAI) PROMs, compared to AS with current IBP. PsA with current IBP received pharmacological, anti-rheumatic, treatment more frequently than AS with current IBP, while AS and other SpA received treatment to a similar degree. Conclusion: The proportion of patients with current IBP was substantial in all three groups and health reports in the non-AS groups were similar or worse compared to the AS group supporting the severity of IBP in these non-AS SpA groups. These findings may indicate a room for improvement concerning detection of axial disease within different subtypes of non-AS SpA, and possibly also for treatment.