People under the age of 45 with chronic back pain for more than 3 months can be reliably identified as having axial spondyloarthritis (axSpA) if they have one or more of three SpA disease features, researchers report in Arthritis & Rheumatology.
The research team, led by rheumatologist Dr. Atul Deodhar from Oregon Health & Science University in Portland, noted that results of the German MASTER study indicated that among undiagnosed patients with chronic back pain starting before the age of 45 the presence of inflammatory back pain, human leukocyte antigen B27 (HLA-B27), and/or sacroiliitis on imaging was a reliable screening method for axSpA.
Dr. Atul Deodhar
However, the authors said, there is limited information on the epidemiology of axSpA, which encompasses ankylosing spondylitis (AS) and nonradiographic axSpA (nr-axSpA), in the United States. Both AS and nr-axSpA typically go undiagnosed for many years, but AS is more easily identified by the presence of sacroiliitis on radiographs.
In order to determine if the German research finding applied to the U.S. population, the researchers conducted the Prevalence of Axial SpA (PROSpA) trial, involving 751 patients from 68 rheumatology centers who were either existing patients in rheumatology practices, new referrals, or were self-referred.
Participants were required to have chronic back pain for 3 or more months beginning at less than 45 years of age and have one or more of three SpA features: 1. positive HLA-B27; 2. current inflammatory back pain; and 3. MRI/x-ray evidence of sacroiliitis, and no prior SpA diagnosis.
Medical history/physical exam, pelvic x-ray, MRI of sacroiliac joints, C-reactive protein, and HLA-B27 were collected and rheumatologists were asked if a clinical diagnosis of axSpA could be made based upon results.
Results showed that out of a total of 697 patients, 319 (46%) were given a clinical diagnosis of axSpA by the rheumatologist (Arthritis Rheumatol. 2016 Jan 27. doi: 10.1002/art.39612).
Of 744 patients, 348 (47%) fulfilled Assessment of SpondyloArthritis International Society (ASAS) criteria. Of these, 238 were classified as nr-axSpA, and 108 were classified as having AS based on fulfillment of the modified New York criteria. (Two patients had missing data.)
Additionally, 238 (32%) patients were categorized as having nr-axSpA, and 396 patients did not fulfill ASAS criteria or the modified New York criteria for AS.
The specificity and sensitivity of the ASAS criteria are reported at 84% and 83%. About 80% of the patients who received a clinical diagnosis of axSpA also fulfilled the ASAS axSpA criteria. The specificity and sensitivity of the criteria in this study were 79% (95% confidence interval, 75%-83%) and 81% (95% CI, 77%-85%), respectively.
The researchers noted that the majority of patients who received a diagnosis from a rheumatologist fulfilled the imaging arm of the ASAS criteria, whereas those who did not receive a diagnosis fulfilled the clinical arm.
“This observation highlights the need for accurate interpretation of MRI images in clinical practice given the importance of MRI imaging for evaluation of patients for axial SpA,” they wrote.
Overall, the findings emphasized the need to improve the identification and diagnosis of both AS and nr-axSpA among patients already receiving care in rheumatology practices and those newly referred to rheumatologists, the researchers said.
“These patients experience similar burden of disease and can remain undiagnosed, and therefore, untreated, for many years,” they wrote.
Indeed, the data indicated that some of the patients included in the study had symptoms for an average of 14 years, they said.