Psoriatic Arthritis
The joint side of psoriasis, and the second post in our spondyloarthritis series.
This is the second post in our spondyloarthritis series. Last time was the overview. Today is psoriatic arthritis, which is one of the most common conditions in the group and one I see often in clinic.
Psoriatic arthritis, or PsA, is inflammatory arthritis that occurs in people with psoriasis. The same immune dysfunction that drives the skin disease can also drive inflammation in the joints, the tendons, and the spine.
About 1 in 3 people with psoriasis will develop PsA at some point. In the vast majority of cases, the skin disease comes first. Joint symptoms usually appear years after the psoriasis, which is part of why the link is often missed. Many patients and providers do connect it, but plenty don't, and PsA stays underdiagnosed as a result.
A smaller group develops the joint disease first, or both at the same time. And rarely, people develop PsA without significant skin findings at all.
What it looks like
One of the challenging things about PsA is that it doesn't have a single typical presentation. It can look very different from one patient to the next. The patterns I look for:
Peripheral joint inflammation. Swelling and stiffness in the small joints of the hands and feet, or larger joints like the knees and ankles. Often asymmetric, unlike RA.
Dactylitis. A whole finger or toe diffusely swollen, often described as a "sausage digit." This finding is fairly specific to spondyloarthritis when you see it.
Enthesitis. Inflammation where tendons attach to bone. Common spots include the Achilles tendon, the elbows, and around the knees. Patients often describe this as a pain that won't go away in one specific spot.
Spine involvement. Some patients develop inflammatory back pain similar to ankylosing spondylitis. Worse in the morning, improves with movement.
Nail changes. Pitting, ridging, or separation of the nail from the nail bed (onycholysis). These can be subtle but often track with joint disease activity.
Most patients don't have all of these. But the combination of psoriasis (even mild or in remission) and any of these patterns is worth a closer look.
Why it gets missed
A few reasons PsA is underdiagnosed:
The skin and the joints are managed by different specialists. Dermatology is treating the psoriasis. Primary care is hearing about the joint pain. The dots don't always get connected.
Joint symptoms get attributed to other things. Osteoarthritis, overuse, gout, fibromyalgia. Some of those can coexist with PsA, which makes it even harder to sort out.
The presentation is variable. There isn't one classic look.
And the labs don't always help. Unlike rheumatoid arthritis, there's no single blood test that confirms PsA. Inflammatory markers can be elevated, but they can also be normal, especially when only a few joints are involved.
Diagnosis
PsA is a clinical diagnosis. It comes from putting the picture together: the history of psoriasis (sometimes subtle, sometimes years in the past), the pattern of joint and tendon involvement, the exam findings, and supportive labs and imaging when helpful.
I'll often order labs to rule out other things (rheumatoid factor, anti-CCP, uric acid for gout), check inflammatory markers, and sometimes get X-rays or musculoskeletal ultrasound to look for characteristic findings.
The history of psoriasis is a big clue, even when the skin disease is mild or in remission. I'll ask about scalp psoriasis, nail changes, or scaly patches that have come and gone, because those can all count even if the patient doesn't think of them as significant.
Treatment
PsA is treatable, and the treatment landscape has expanded significantly over the past 15 years. The goals are the same as in any inflammatory arthritis: control inflammation, prevent joint damage, and improve quality of life.
For milder disease, we often start with anti-inflammatories and traditional DMARDs. Methotrexate is the most common. It's a reasonable option for joints when the skin disease is mild, although it's not the best agent for skin. In practice, our hands are sometimes tied here, because insurance will often require a trial of methotrexate before approving a biologic, regardless of clinical judgment.
For moderate to severe disease, or disease that isn't responding to traditional DMARDs, we have a range of targeted biologic and oral medications. A few of the categories:
TNF inhibitors. Adalimumab (Humira), etanercept (Enbrel), infliximab (Remicade), golimumab (Simponi), and certolizumab pegol (Cimzia). The longest track record in PsA.
IL-17 inhibitors. Secukinumab (Cosentyx), ixekizumab (Taltz), and bimekizumab (Bimzelx). Strong for both skin and joints.
IL-23 inhibitors. Guselkumab (Tremfya) and risankizumab (Skyrizi). Also strong on skin and joints.
IL-12/23 inhibitor. Ustekinumab (Stelara).
JAK inhibitors. Tofacitinib (Xeljanz) and upadacitinib (Rinvoq). Oral pills, useful when injections aren't a fit.
I'll do a deeper dive on each of these medication groups in future posts, since each class has its own nuances around when we use it, what to watch for, and how it fits into the broader treatment picture.
One of the real advantages in PsA is that many of these medications treat both the skin and joint disease, which simplifies things for patients who would otherwise need separate treatment plans for each.
Early treatment matters. PsA can cause joint damage over time if it's not controlled, and that damage is often irreversible. The sooner we identify it and start treatment, the better we protect the joints.
Why this matters
Spondyloarthritis is common, often missed, and very treatable when caught early. Like other inflammatory arthritis, it can cause joint damage and disability if not controlled. And like other autoimmune conditions, it's a clinical diagnosis that comes from putting the full picture together.
A few things that should raise the question of spondyloarthritis:
Young patient with chronic back pain that's worse in the morning and better with movement
Someone with psoriasis who develops joint pain or swelling
Heel pain that won't go away
A swollen finger or toe with no obvious injury
Joint pain in someone with inflammatory bowel disease
The bottom line
If you have psoriasis and you're dealing with joint pain, swelling, stiffness, or unexplained pain in a specific spot, don't dismiss it. The connection between psoriasis and joint disease is real, common, and treatable.
Next up in the series: ankylosing spondylitis.
