Clinical Manifestations. Most people who develop psoriatic arthritis have skin symptoms of psoriasis first; however, in 15% of people symptoms of arthritis may appear before the diagnosis of psoriasis. There are various patterns of psoriatic arthritis, and some patients may have overlapping patterns:

• Distal arthritis—predominantly affects distal joints of the fingers and toes and can be frequently accompanied by arthritis in a few large joints such as the knee or ankle (5% of the patients)

• Oligoarthritis—affecting four or fewer joints, often in an asymmetric distribution (70% of the patients)

• Symmetric polyarthritis—affects five or more joints on both sides of the body; may be difficult to distinguish from rheumatoid arthritis (15% of the patients)

• Spondylitis variant—affects the joints of the spine as well joints peripherally, which can be similar to ankylosing spondylitis

• Arthritis mutilans—destructive and mutilating changes of the phalanges adjacent to the inflamed joints (5% to 25% of the patients)

In addition, there are extra-articular manifestations:

• Enthesitis—inflammation at the site of tendon insertion into bone

• Dactylitis (sausage digit)—diffuse swelling of the entire finger or toe

• Tenosynovitis (tendonitis)—inflammation that may affect the flexor tendons of the fingers, the extensor carpi ulnaris, and other sites

• Nail lesions (pitting, onycholysis)

Radiographic Findings/Laboratory Studies. There are no specific laboratory tests for the diagnosis of psoriatic arthritis, but there are some important considerations when a patient with psoriasis presents with inflammatory arthritis:

• Typically the rheumatoid factor and anti-CCP antibody studies are negative, unless there is an overlap with rheumatoid arthritis.

• HLA-B27 is present in some patients.

• The joint pattern often affects distal interphalangeal joints, unlike in rheumatoid arthritis, which usually affects the metacarpophalangeal joints. Osteoarthritis may affect both distal and proximal interphalangeal joints and may be inflammatory.

Typical radiographic features of psoriatic arthritis include a characteristic pattern of bone resorption/erosion, hyperostosis, fusion, enthesopathy, and predilection for the distal phalanx.

Bone resorption/erosion in psoriatic arthritis is not always marginal (as in rheumatoid arthritis) and may involve the entire articular surface, which leads to joint space widening and the late stage of “pencil-in-cup” deformity.

Hyperostosis is a common and distinctive feature of psoriatic arthritis with increased sclerosis of the trabecular bone, fluffy bony productive changes around the erosions or away from the articulation (e.g., radial styloid), and periostitis along the small bones of hands and feet.

Enthesopathy is common at the calcaneal attachments of the plantar aponeurosis and Achilles tendon and is characterized by ill-defined erosion and surrounding hyperostosis.

Distal phalanx involvement is usually associated with nail disease. Typically seen are osteolysis and hyperostosis. Diffuse hyperostosis of a phalanx is called an ivory phalanx that is virtually pathognomonic of psoriatic arthritis.

Involvement of an entire digit or toe (dactylitis, sausage finger) is due to underlying tenosynovitis and involvement of the periarticular structures.

Involvement of the axial skeleton is common in psoriatic arthritis with radiographic features of spondylitis and sacroiliitis, similar to that in ankylosing spondylitis, but, in general, less diffuse and severe with a propensity for thick, irregular syndesmophytes.

Treatment. There is no cure for psoriatic arthritis, but there have been significant advances in treatment. Treatment can range from physical therapy and NSAIDs to help relieve the joint pain and stiffness symptoms to more aggressive treatment with DMARDs to slow and sometimes halt the progression of the destructive joint disease, especially when treatment is started early in the disease course. Patient screening questionnaires are now available to help diagnose psoriatic arthritis earlier in patients with psoriasis.

• Physical and occupational therapy as well as exercise may help to relieve the pain and stiffness and to maintain joint function.

• NSAIDs can be used in combination with DMARDs to help to control inflammation and relieve the pain from psoriatic arthritis. NSAIDs must be taken continuously and at a sufficient dose to have an anti-inflammatory effect. These agents do not slow the progression of the arthritis.

• DMARDs should be used early in patients with aggressive and potentially destructive joint disease. DMARDs that should be considered include methotrexate and anti–TNF-α inhibitors (also known as biologic DMARDs).

• Biologic DMARDs work primarily by blocking or neutralizing the effects of TNF-α, which is thought to be overexpressed in patients with psoriatic arthritis. These agents usually work rapidly, often within 2 to 4 weeks, and may be used alone or in combination with other DMARDs such as methotrexate.

• Intra-articular and low-dose glucocorticoids (corticosteroids) may be used to suppress inflammation and relieve pain until the treatment with DMARDs is established. Oral glucocorticoids should be avoided due to the chance of developing worsening psoriasis.

A family history of psoriasis, extensive skin involvement, disease onset age younger than 20 years, expression of HLA-B27, HLA-B39, or other alleles, and polyarticular and erosive disease may be factors that are predictive of a worse prognosis. It is also important to screen for psoriatic arthritis in patients with psoriasis to help ensure early diagnosis.