A deeper look into axial spondyloarthritis: Prevalence, diagnosis, and treatment

There is a large diagnostic delay for people with axial spondyloarthritis (axSpA). In 2008, the SPACE cohort started to assess the prevalence of axSpA – and the reliability of an early diagnosis in people with chronic back pain (CBP). Everyone taking part was under the age of 45, and with recent-onset CBP (over 3 months, and up to 2 years) of unknown origin. Now, Marques and colleagues present two abstracts of the 2-year primary outcome of the study at the EULAR congress.

The first abstract assesses the 2-year prevalence of an axSpA diagnosis among people with recent onset CBP who had been referred to a rheumatologist and investigates the sustainability of a baseline diagnosis when reviewed after 2 years. Across 555 people with CBP, 175 received a diagnosis of definite axSpA at baseline, and 165 had received the same by 2 years. This means that one-third of people with recent-onset CBP referred to a rheumatologist has definite axSpA.

The SPACE researchers showed that diagnostic judgments remained relatively stable: after 2 years, only 5% of the original definite axSpA diagnoses were refuted, while 8% of people 'gained' a definite axSpA diagnosis. As expected, features related to SpA were more prevalent in the definite axSpA diagnosis group when compared to no axSpA or uncertain diagnosis groups (group definitions based on the diagnosis at 2 years) – with the presence of imaging-detected sacroiliitis at baseline being the best discriminator.

These findings are important, because they suggest that most people with recent-onset CBP can be reliably diagnosed at their first assessment. However, it is important to note that residual diagnostic uncertainty remained in 15% of people with CBP. This diagnostic uncertainty can be an obstacle to initiating disease-modifying treatment, so it is important to understand the value of repeated assessments of SpA features for a definite clinical diagnosis.

In their second SPACE abstract, Marques et al. assessed the yield of repeat assessments over 2 years and described the characteristics in people whose diagnosis changed over time. Over the course of the study, the diagnosis changed to definite axSpA in 32 patients. Of these, 16 had been ascribed uncertain axSpA at baseline, 11 were uncertain no axSpA, and 5 were definite no axSpA. On average, three or four SpA features were already present at baseline in this group, and one new feature developed over the 2-year follow-up. Interestingly, imaging findings and response to NSAID appeared as frequent features that potentially contribute to making a new definite axSpA diagnosis over time.

SPACE is not the only cohort taking a deeper look at axSpA. Previous studies have suggested there could be regional differences in axSpA clinical phenotypes. To explore this, IMAS – the International Map of Axial Spondyloarthritis – is looking at these differences in 27 countries across 5 regions globally. The results show significant differences between regions in a variety of characteristics. This includes age at onset of symptoms, with the highest in Latin America. When considering diagnostic delay, this was found to be longest in South Africa and lowest in Asia. The lowest frequency of HLA-B27 positivity was observed in Latin America and the highest in Asia. Family history of SpA was most often recorded in Europe and less often in Asia. All extra-musculoskeletal manifestations included were lowest in Europe compared with other regions. Finally, physical and mental comorbidities were frequent in African patients and less common in Europe and Asia. In the full abstract, the group also report on mean disease activity, spinal stiffness, and functional limitations. Further understanding of these regional differences is needed to achieve early diagnosis and initiate timely treatment in people with axSpA