DENVER (FRONTLINE MEDICAL NEWS) – Only one-quarter of patients newly identified as having nonradiographic axial spondyloarthritis will progress to ankylosing spondylitis within 15 years, according to findings from the Rochester (Minn.) Epidemiology Project.

Disease progression occurred far more frequently and rapidly in patients who qualified for nonradiographic axial spondyloarthritis (nr-AxSpA) on the basis of positive pelvic MRI findings than in those who met only the clinical criteria for nr-AxSpA, Dr. Runsheng Wang reported at the annual meeting of the Spondyloarthritis Research and Treatment Network.

The Rochester Epidemiology Project is a unique health care research resource. Essentially all residents in Olmsted County, Minn., the home of the Mayo Clinic, have signed off on participation in the project. Dr. Weng’s study focused on 16- to 45-year-old county residents who reported new-onset chronic back pain during 1985-2010, none of whom showed the radiographic evidence of sacroiliitis required for a diagnosis of ankylosing spondylitis.

The study began with 1,142 patients who for a variety of reasons underwent a pelvic MRI. Eighteen of them ultimately met ASAS (Assessment of Spondyloarthritis International Society) imaging criteria for nr-AxSpA. They formed the imaging arm of the study.

Another 1,009 patients in the target age group presented with chronic back pain but no MRI findings. Sixty-five of them were entered into the clinical nr-AxSpA arm of the study on the basis of being positive for HLA-B27, explained Dr. Wang, a clinical scholar in rheumatology at the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

Subjects were followed for a mean of 10.7 years. The overall rate of progression from nr-AxSpA to ankylosing spondylitis was 6.4% at 5 years, 17.3% at 10 years, and 26.4% at 15 years.

These data help fill an unmet need regarding understanding of the prognosis of nr-AxSpA. The two previous studies by other investigators have limitations: one German study showed an 11.2% rate of conversion to ankylosing spondylitis but was limited to 2 years of follow-up ( Ann Rheum Dis. 2011 Aug;70[8]:1369-1374 ), while a Norwegian study comprising 20 patients showed a 20% progression rate over 8 years, Dr. Wang noted.

In her Minnesota study, patients who met criteria for nr-AxSpA based upon MRI criteria were 3.5-fold more likely to progress to ankylosing spondylitis with evidence of sacroiliitis on X-ray, compared with those in the clinical arm. There was a hint of a gender difference: Men were 1.58 times more likely to progress to ankylosing spondylitis than were women. However, this difference didn’t reach statistical significance.

Audience members were particularly interested in whether the Minnesota data demonstrated that treatment with NSAIDs and other agents had an impact upon the progression rate. Dr. Wang replied that the study size was simply too small to allow for a reasonable multivariate analysis examining this key question.

The National Institutes of Health funded the study. Dr. Wang reported having no financial conflicts of interest.