Neal Birnbaum, MD, on Nonradiographic axSpA: Part 1
In part 1 of a 2-part podcast, Dr Birnbaum provides an overview of the differences and similarities of nonradiographic axial spondyloarthritis and ankylosing spondylitis, including indicators to help distinguish between these conditions on diagnosis.
Neal Birnbaum, MD, is chief of rheumatology at California Pacific Medical Center in San Francisco, California.
TRANSCRIPT:
Welcome to this podcast from the Rheumatology and Arthritis Learning Network. I'm your moderator, Rebecca Mashaw, and I'm here today with Dr. Neal Birnbaum, who is the chief of Rheumatology at California Pacific Medical Center in San Francisco. We're going to be talking about nonradiographic axial spondyloarthritis and how it differs from or if it does differ from ankylosing spondylitis or AS. Thanks for joining us today, Dr. Birnbaum.
Dr. Neal Birnbaum:
Thank you for having me.
RALN:
First of all, let's talk about what distinguishes nonradiologic-axSpA from other axial spondyloarthropathies.
Dr. Birnbaum:
They're a group of illnesses that fall under the general term of spondyloarthropathies, actual inflammatory disease, HLA-B27 related problems. The traditional one, ankylosing spondylitis, was kind of the classic one. If one goes back to the old 1984, I believe was the date, for the modified New York criteria to diagnose spondylitis, they required radiographic change in the sacroiliac joints, plain radiographs. The term nonradiographic axial spondyloarthropathy came up starting somewhere around 2009 to describe patients who had typical inflammatory back pain and yet did not have radiographic change on plain x-ray.
RALN:
Are there differences in the symptoms that you see in patients who have the nonradiographic form and the classic ankylosing spondylitis?
Dr. Birnbaum:
Not really. There's a question of severity. The patient who's got far advanced spondylitis, with not only sacroiliac joint changes but spinal changes, may have markedly diminished spinal range of motion but the story of inflammatory pain is the same. What's the story of inflammatory pain? Nighttime pain, morning stiffness, better with activity. If you look at the usual classification criteria, remember that classification criteria are different from diagnostic criteria; the classification criteria used to enroll people in clinical trials, to make sure that everybody at all these different centers around the world are enrolling the same people.
The classification criteria usually are someone whose onset of symptoms before age 40 or 45, gradual onset of symptoms, and then the characteristic, again, inflammatory back pain story, nighttime pain, morning stiffness, better with activity. Those are really the same, whether the patient has radiographic changes or doesn't have radiographic.
RALN:
Is the lack of joint damage seen on x-rays the primary distinguishing factor between the nonradiographic form of the disease and ankylosing spondylitis?
Dr. Birnbaum:
Yes. If you talk about how do you make the diagnosis of nonradiographic disease, how do you make that diagnosis since there aren't plain x-ray changes, then there's certain criteria. The 2 ones that really stand out, one is the presence of the HLA-B27 antigen, the genetic marker for spondylitis that's present in about 6% of the general population but in 70 to 90% of people who have a spondyloarthropathy, so that's one. If you have the classic story of inflammatory pain plus B27, then that's a way to diagnose nonradiographic-axSpA, and the other is the idea of MRI changes. MRI changes with juxta-articular edema near the sacroiliac joints has come into play as the other way to look at nonradiographic, nonradiographic meaning nonplain x-ray, but positive MRI, to make the diagnosis of a spondyloarthropathy.
RALN:
So those are the two key factors that a rheumatologist should be considering when trying to make this diagnosis.
Dr. Birnbaum:
There are some others that play a role. Are the measures of inflammation elevated, the sed rate and CRP? They may be, and that's certainly nice if they are, but certainly there are other patients who have normal sed rate and CRP. Do patients have other symptoms that suggest a spondyloarthropathy? Is there a history of iritis? Is there a history of psoriasis? Is there a history of inflammatory bowel disease? Do they have a history of peripheral arthritis or enthesopathies or dactylitis, anything that suggests a systemic inflammatory disorder?
RALN:
How easy is it now for a practicing rheumatologist to get the HLA test, for instance?
Dr. Neal Birnbaum:
Yeah, that's a standard lab test, any commercial lab is going to have that.
RALN:
That and the MRI, those two are major steps toward making that diagnosis?
Dr Birnbaum:
Correct. Those are things that may be done also by a primary care doctor. It doesn't have to be a rheumatologist, depending on the expertise of the primary care doctor. When I go around and lecture to primary care doctors, what I'm usually trying to get them to think about is inflammatory back pain. How do you differentiate inflammatory back pain from mechanical back pain? If they're comfortable doing that, I'm happy. If they want to go and carry the diagnostic studies a little bit further, certainly a plain x-ray of the sacroiliac joints and an HLA-B27 are pretty simple and inexpensive things to do.
RALN:
How do you make that distinction between inflammatory and mechanical back pain?
Dr. Birnbaum:
Inflammatory back pain is usually insidious in onset, younger age, and prominent pain at night, interrupting sleep, very stiff in the morning and better once you get up and get moving. The story of mechanical back pain is the opposite. The patient usually feels not too bad when they first wake up but once they've been up all day doing activities, carrying weight around, if they're being upright, they tend to feel worse.
RALN:
You mentioned several other conditions, and that is a good segue to the next question which is, are some people at higher risk of developing axial disease, whether it's nonradiographic or ankylosing spondylitis? You mentioned some other factors, enthesitis, peripheral arthritis, inflammatory bowel disease, other autoimmune conditions. Is that a risk factor?
Dr Birnbaum:
Yes, particularly psoriatic arthritis. Many, many years ago, I wrote a paper on tissue typing in psoriatic arthritis and we were able to show there is some increase in HLA-B27 incidents in patients with psoriatic arthritis, and those were the patients who developed spinal involvement. If you just took patients who had only peripheral joint psoriatic arthritis and no axial involvement, their rate of B27 was the same as the general population.
Please be sure to join us as I continue my conversation with Dr. Neal Birnbaum on therapy for nonradiologic axial spondyloarthritis.
