Psoriatic arthritis: Clinical sciences

Psoriatic arthritis, or PsA for short, is a type of autoimmune arthritis that’s associated with a chronic inflammatory skin disorder known as psoriasis. In psoriatic arthritis, inflammation leads to joint erosion and destruction, causing joint pain, swelling, and stiffness.

The assessment of patients with psoriatic arthritis involves Classification criteria for Psoriatic Arthritis, or CASPAR, which is a validated clinical tool used for diagnosis.

Okay, let’s look at a patient presenting with a chief concern suggesting psoriatic arthritis. The first step is to perform a focused history and physical examination. You should also order labs including rheumatoid factor, or RF, antinuclear antibodies, or ANA, C-reactive protein, or CRP, and erythrocyte sedimentation rate, or ESR for short. Additionally, you should obtain X-rays of any affected joints.

Your patient will typically report joint pain, stiffness, and swelling most commonly in the fingers and toes. Psoriatic arthritis often targets the small joints of fingers and toes, but it can affect any joint. So don’t forget to ask about pain, stiffness, and swelling in larger peripheral joints like knees and elbows, and even in axial joints like spinal intervertebral and sacroiliac joints.

They may also have a personal or family history of psoriatic skin lesions. These present with dry, thick, and silvery-white scales, as well as a positive Auspitz's sign, which is the appearance of punctate bleeding spots when psoriasis scales are scraped off.

Moving on, physical exam findings typically reveal joint tenderness and effusion, as well as dactylitis, sometimes described as sausage fingers.

You might also notice scaly erythematous plaques on the scalp, extensor surfaces of the limbs, and perineum. Other findings may include pitting of the nails.

Lab results will reveal a negative rheumatoid factor and ANA, and may show elevated CRP and ESR. Additionally, you will see positive HLA-B27 in around 10% of your patients!

Now, here’s a clinical pearl! The laboratory workup for autoimmune or inflammatory arthritis can be quite extensive.

You may need additional labs, such as c-ANCA and p-ANCA, anti-cyclic citrullinated peptide, and uric acid. Additionally, you might need to check Lyme disease serologies, complement levels, and joint fluid analysis.

These tests can help you rule out other rheumatologic disorders, since they are typically negative in psoriatic arthritis!

For the X-ray findings, you might notice joint space narrowing, or joint margin ossification, also known as juxta-articular new bone formation. In severe cases, there might be arthritis mutilans, which appears on X-rays as a pencil-in-cup deformity.

At this point, you should suspect psoriatic arthritis!

Okay, once you suspect psoriatic arthritis, your next step is to assess the patient for the CASPAR criteria, which is a validated clinical tool commonly used to assess psoriatic arthritis. To fulfill the CASPAR criteria, a patient must score 3 or more points based on the following 5 clinical findings.

First, there should be evidence of psoriasis, such as current psoriatic skin changes, or personal history or family history of psoriasis. The second one is current psoriatic nail changes like onycholysis, while the third is negative lab testing for rheumatoid factor. Fourth is current or past history of dactylitis, and fifth is radiographic evidence of juxta-articular new bone formation.