Psoriatic arthritis can have a diverse presentation not only with the affected joints, but also involving nails, tendons, and ligaments. An entire digit of the hand or foot can become swollen, known as dactylitis, or “sausage digit.” Inflammation at the insertion of tendons or ligaments, known as enthesitis, is also seen in PsA. Most common sites include the Achilles tendon, plantar fascia, and ligamentous insertions around the pelvic bones. 3 Nail changes that are typically seen in patients with psoriasis can be seen in PsA as well, including pitting, ridging, hyperkeratosis, and onycholysis. 3 Ocular inflammation which is classically seen with other spondyloarthropathies, can be seen in patients with PsA as well, frequently manifesting as conjunctivitis. 2,3
Psoriatic arthritis is commonly classified under the broader category of seronegative spondyloarthropathies, given the low frequency of a positive rheumatoid factor. 3 Currently, there are no laboratory tests that can help with a PsA diagnosis. 3 Acute-phase reactants such as erythrocyte sedimentation rate and C-reactive protein may be elevated, indicating active inflammation.
Radiographic data, such as X-rays of the hands and feet, can confirm the clinical distribution of joint involvement and show evidence of erosive changes. Further destructive changes include osteolysis (bone resorption) that may cause the classic pencil-in-cup deformity, typically seen in arthritis mutilans (Figure 1). 3 Other radiographic evidence of PsA can include proliferative changes with new bone formation seen along the shaft of the metacarpal and metatarsal bones. 3 Patients with axial involvement can have evidence of asymmetric sacroiliitis, which can be seen on radiographs. Asymmetric syndesmophytes, or bony outgrowths, can also be seen throughout the axial spine. 3
Diagnosis is based on the history and clinical presentation of a patient with the help of laboratory work and radiographs. Other forms of arthritis (such as rheumatoid arthritis, crystal arthropathies, osteoarthritis, ankylosing spondylitis) should be excluded. Given the varied presentation of PsA, classification criteria have been developed to assist in clinical research. Classification Criteria for Psoriatic Arthritis (CASPAR) have been developed and validated as an adjunct to clinical diagnosis and a source for clinical research (Table 1). 7 Musculoskeletal pain in patients with psoriasis can be due to causes other than PsA, such as osteoarthritis and gout. A close working relationship in a combined rheumatology/dermatology clinic is vital to providing optimal diagnostic and treatment care for patients with psoriasis and PsA. 8
The etiology of PsA is currently unknown, although many genetic, environmental, and immunologic factors have been identified that play a role in the pathogenesis of the disease. In this setting, immunologically mediated processes that cause inflammation occur in the synovium of joints, enthesium, bone, and skin of patients with PsA. 9 Studies have shown that activated T cells and T-cell–derived cytokines play an important role in cartilage degradation, joint damage, and stimulating bone resorption. 9
One particular proinflammatory cytokine, tumor necrosis factor alpha (TNFα), has been the target for many treatment modalities for several years. With new and ongoing research into the PsA pathogenesis, other treatment options have been discovered, targeting different cytokines and T cells that are involved in the disease process. This has led to drug trials and recent FDA approvals of several new medications, which provide further options for clinicians in managing and treating PsA.