Differential Diagnosis for Rheumatic Diseases

Sergio Schwartzman, MD: With regard to differentiating the 3 most common inflammatory arthritides— these are rheumatoid arthritis, psoriatic arthritis, and axial spondyloarthritis/ankylosing spondylitis—there is an overlap in that all 3 disease groups can affect the peripheral joints. But they differ in that rheumatoid arthritis, for reasons that are not that clear to me, most commonly tends to affect the small points of the hands and the feet but can affect any joint. It tends to exclude the sacroiliac joints and the spine, other than the cervical spine. The cervical spine can be involved with rheumatoid arthritis. Although tendinitis/enthesopathy can happen in patients with rheumatoid arthritis, it’s not 1 of its common features.

Patients who present predominantly with small joint involvement that’s symmetric, and don’t have features of other rheumatic diseases, will most likely have rheumatoid arthritis. As mentioned previously, this could be supported by checking a rheumatoid factor or CCP [cyclic citrullinated peptide] antibody, or imaging studies that show a classic finding.

Rather than calling it psoriatic arthritis, I call it psoriatic disease, is a much different entity. Back in 1974, there were a set of criteria that were devised by 2 rheumatologists, John Moll and Verna Wright. These were the Moll and Wright classification criteria for psoriatic arthritis. They included very different phenotypes. The phenotypes that were included were an oligoarticular form, which is 4 or less joints; a polyarticular form, which is more than 4 joints; a mutilans form, which is very classic for psoriatic disease where you have telescoping of the digits and complete destruction of joints; and then an axial form that tended to affect predominantly the sacroiliac joints, but it could affect the spine in any location and tended to be asymmetric.

Psoriatic arthritis, from the perspective of clinical differentiation from rheumatoid arthritis, can have all of those patterns. Again, just being focused on the musculoskeletal element here, axial disease or sacroiliac disease would not be common at all in rheumatoid arthritis, but it is 1 of the Moll and Wright subtypes of psoriatic disease. Additionally, psoriatic disease tends to have much more enthesitis than rheumatoid arthritis.

The last entity, axial spondyloarthritis, as the name implies, really focuses on the axial skeleton. We’ve subdivided this into nonradiographic and radiographic disease. But generally, it does tend to have sacroiliac involvement. From a strictly musculoskeletal perspective, these 3 entities really have different presentations. I should say that axial spondyloarthritis also has enthesitis as 1 of its components.

The other way to differentiate between these conditions is that their extra-articular manifestations are very different. For example, in rheumatoid arthritis you can have ocular involvement, and that involvement tends to be scleritis. You can have pulmonary disease, which is less common in ankylosing spondylitis, or axial spondyloarthritis, or psoriatic arthritis. You can have nodular disease, the rheumatoid nodule, which does not happen in ankylosing spondylitis, or in psoriatic arthritis.

Psoriatic disease overlaps a little bit more with axial spondyloarthritis in terms of its extra-articular manifestations. Clearly psoriasis is present in most patients who have psoriatic arthritis, although not all. It is much less common in rheumatoid arthritis. Even though it can be seen in axial spondyloarthritis, it is much less common as well.

Patients with psoriatic arthritis can also have ocular involvement, and that is a completely different presentation in patients with rheumatoid arthritis. They tend to have uveitis. The differentiation point between the uveitis that patients with psoriatic arthritis have, and axial spondyloarthritis, or ankylosis spondyloarthritis, that patients have is that the type of uveitis is different. Patients with ankylosing spondylitis and axial spondyloarthritis have an acute anterior recurrent uveitis, whereas patients with psoriatic arthritis can have that, but they can also have intermediate panuveitis and posterior uveitis. It can be chronic.

The differential diagnosis, in summary, really focuses across 3 different lines. The first is that the type of musculoskeletal involvement in these 3 diseases is different. The second is that there are extra-articular manifestations that can help you differentiate between these. One that I neglected to say, but that I should add, is inflammatory bowel disease. Inflammatory bowel disease is very common in patients with axial spondyloarthritis, much less common in psoriatic disease, and nonexistent as a manifestation in rheumatoid arthritis. So, these extra-articular manifestations help us with the differential diagnosis.

The third point that I wanted to make is that sometimes there is overlap. As we think about these diseases, although we try to categorize them into very specific disease processes, sometimes our immune system doesn’t behave that way.

Transcript edited for clarity.