Prevalence of nr-axSpA

Transcript: Sergio Schwartzman, MD: In terms of numbers, Atul, can you comment a little bit on the prevalence of this disease in our community? Any data on the incidence of that as well would be helpful. What numbers are we dealing with?

Atul Deodhar, MD, MRCP: In 2009 when the ASAS [Assessment of Spondyloarthritis international Society] criteria came out, approximately the same time in the United States, there was a large population-based analysis that was done. This is the NHANES study, National Health and Nutrition Examination Survey, which any way happens every 2 years. In 2009 and 2010, SPARTAN [Spondyloarthritis Research and Treatment Network] collaborated with the NHANES federal government the study. They looked at how common back pain is in the United States on a population basis.

How common is inflammatory back pain in the United States? What's the prevalence of HLA-B27 [human leukocyte antigen B27] in the United States? Finally, how common is axial spondyloarthritis and the United States? This was the same year when ASAS was developing their clinical classification criteria. The classification criteria used in this particular survey were older criteria called ESSG or European

Spondyloarthropathy Study Group criteria or Amor criteria, which were…a year before that.

In any case, what was found was that axial spondyloarthritis, the bigger term, is between 0.92% to 1.4% of the US population. Chronic back pain is about 20% of the US population. Chronic back pain is back pain for 3 months or longer at a time. Inflammatory back pain is about 7%—6.9% of the US population has that. The total population with axial spondyloarthritis is 0.9% to 1.4%, say 1% of it.

When the question was asked to the population—this is population-based to the people participating in the survey—that has anybody told them that they have ankylosing spondylitis, approximately 0.55% of the people said, “My provider has told me that I have ankylosing spondylitis.” This is very interesting because a similar enhanced survey was done back in the 1970s. They in fact did x-rays on those people back in the 70s. The x-rays were read by radiologists. There again, 0.5% of the US population were found to have definitive sacroiliitis.

I would like to believe in this number that 0.5% have ankylosing spondylitis and 1% have axial spondyloarthritis, so that makes the prevalence of non-radiographic axial spondyloarthritis also 0.5. It is equal—it is as big as ankylosing spondylitis. I want to get back to 1 of the points that Philip raised, and that's about the spectrum. This is now another confusion in the minds of people and rheumatologists.

This really is a spectrum—nonradiographic is at 1 end of the spectrum, ankylosing spondylitis at the other end of the spectrum. It doesn't necessarily mean that people have to go from 1 end of the spectrum to the other end of the spectrum. Not every spectrum the patients move from 1 end to the other. People can stay where they are. Some people will progress from nonradiographic to radiographic. There is no question nonradiographic is at 1 end of the spectrum.

Bamboo spine would be the other end of the spectrum. Of course, bamboo spine is very different situation where people cannot bend and tie their shoes. But beyond that particular very extreme, the overall burden of the disease is very similar whether they have definitive sacroiliac changes or not. Tiffany very nicely told us her personal experience and this has been found in various studies how the functional deterioration or the impact of this disease on work, productivity, how it is very similar on both ends of the spectrum.

The answer again is that prevalence is 0.5% of the general population in the United States. This is different than, of course, diagnostic prevalence which is artificially low. This is because diagnostic prevalence is when people come to your clinic and then you're going to see out of the patients that you have in your clinic, how many have non-radiographic axial spondyloarthritis? Many people with non-radiographic axial spondyloarthritis may not even come to you because they have been missed. So population prevalence is the gold standard.

Sergio Schwartzman, MD: It's interesting. I think 30 years ago we thought that this was a relatively rare group of diseases. But with new classification criteria, this is right up there with rheumatoid arthritis and psoriatic arthritis in terms of the prevalence of the spectrum of the disease group. It'll be interesting to see what the next NHANES study finds now that we've been even more educated.

Transcript Edited for Clarity