Background/Purpose: The concept of inflammatory back pain (IBP) was proposed in association with ankylosing spondylitis (AS), one prototype of Spondyloarthritis (SpA), more than 60 years ago. Spondyloarthritis (SpA) comprises several rheumatic diseases. Although several criteria sets have been developed, the diagnosis of SpA remains challenging. This study aims to evaluate the frequency of inflammatory back pain (IBP) among Brazilian subjects with chronic back pain (CBP), and to describe the results of rheumatologic evaluation based on the axial SpA classification criteria from the Assessment of Spondyloarthritis International Society (ASAS).

Methods:  This was an observational study with retrospective (phase 1) and one-month prospective (phase 2) data collection. Medical records of subjects 18-60 years old, with onset of back pain at age <40 years, and with CBP (pain almost daily ≥3 months), were included in phase 1. Subjects with at least one ASAS screening parameter for IBP were contacted by phone, and confirmed IBP cases were invited to phase 2. At phase 2 visit 1, HLA-B27 and C-reactive protein (CRP) were requested. At phase 2 visit 2, the fulfilment of the ASAS classification criteria for axial SpA was verified. Frequency of IBP among subjects with CBP starting before the age of 40 years was estimated. For subjects included in phase 2, the proportions of positive HLA-B27, AS and non-radiographic axial SpA (nrAxSpA) were calculated.

Results:  A total of 363 records of subjects with CBP were reviewed from five sites. Based on medical records and phone contact, 130 subjects had IBP confirmed (35.8%, 95%CI: 30.9-40.7%). From IBP population, only 52 subjects accepted to participate in phase 2. Mean age was 38.8±11.43 years, 64% were female, 85% professionally active, and 14% had family history of IBP related conditions. Time since CBP onset was 12.3±10.09 years and no subject had a prior diagnosis of SpA. Among the 50 patients that completed visit 2, 14% had positive HLA-B27, 82% had lesions of the sacroiliac joint assessed by MRI, 16% had abnormal clinically significant CRP results, and 10% had grade 3-4 lesions assessed by X-ray. The proportions of AS and nrAxSpA cases were 46% and 26%, respectively by ASAS classification criteria.

Conclusion:  More than one third of the CBP subjects with onset <40 years had IBP by ASAS criteria. Of notice, subjects with a positive HLA-B27 test did not have prior diagnosis of axial SpA. The results in this Brazilian population suggest that patients with IBP may be under diagnosed, delaying their treatment, and that women may seek more for medical care than men. An eventual selection bias cannot be excluded.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/assessment-of-inflammatory-back-pain-and-axial-spondyloarthritis-in-brazil/