Psoriatic arthritis (PsA) is a chronic, seronegative systemic inflammatory arthropathy which is associated with psoriatic skin and nail lesions and characterized by synovitis, enthesitis, dactylitis and spondylitis.
The estimated prevalence varies from 1/5000-1/238 adults in Europe and America to 1/100,000 in Japan. It is not considered a rare disease.
PsA usually presents in the 4-5th decade of life but children (juvenile psoriatic arthritis, see this term) and the elderly can also rarely be affected. In most cases, arthritis appears following a long-standing psoriasis of about 7-12 years, but rarely it can occur at the same time or precede (10-15 % of cases) psoriasis. Psoriasis vulgaris is the most common type of psoriasis seen in PsA but guttate and pustular psoriasis have also been reported. Nail pits and onycholysis occur in 80 to 90% of patients. A wide clinical spectrum is seen between PsA patients but the most frequent manifestations include spondylitis with axial, cervical and thoracic inflammatory pain. Sacroiliitis is usually unilateral but later can become bilateral. Peripheral arthritis can range from monoarthritis to polyarthritis, with oligoarthritis predominating in early disease and polyarthritis more common in later disease. Common additional manifestations include enthesitis, tenosynovitis, and dactylitis. Uveitis is also seen in 4-18% of cases. PsA patients have a higher risk for comorbidities such as hypertension, infections, fatty liver disease, gastrointestinal disease (i.e. Crohn's disease), depression and anxiety.
The exact etiology is unknown but both psoriasis and PsA share common pathogenic mechanisms involving genetic, environmental (i.e. emotional stress, infections, joint trauma, drug use) and immunologic factors. Psoriasis, nail dystrophy, scalp lesions, and intergluteal/perianal psoriasis have been associated with a higher risk of later developing PsA.
PsA is suspected in patients with psoriasis that develop arthritis, enthesitis, dactylitis and/or spondylitis. Family history and a physical exam (tender and swollen joint counts, and a tender entheseal count) help in the diagnosis of PsA. Laboratory testing measuring rheumatoid factor (PsA patients are usually seronegative), anti-cyclic citrullinated peptide antibodies, erythrocyte sedimentation rate and C-reactive protein should also be performed. Radiographs may reveal joint erosions, juxta-articular new bone formation and pencil-in-cup deformity. MRI and ultrasonography can also be performed. The Classification Criteria for Psoriatic Arthritis (CASPAR) are now widely used for the diagnosis of PsA.
Differential diagnoses include rheumatoid arthritis, reactive arthritis, ankylosing spondylitis (see these terms), arthritis of inflammatory bowel disease, gout and osteoarthritis.
Management mainly involves controlling symptoms and preventing joint damage by initiating treatment as early as possible. Nonsteroidal anti-inflammatory drugs (NSAIDs) are a common short-term treatment option for mild PsA. Disease-modifying antirheumatic drugs (DMARDs), such as methotrexate, cyclosporine A and leflunomide have been shown to slow the progression of PsA in some and can be combined with NSAIDs in patients with moderate to severe disease. Anti-tumor necrosis factor agents (i.e. infliximab, etanercept, adalimumab, certolizumab and golimumab) or anti-IL12 agents are also being used in patients with active peripheral or spinal forms of PsA who are intolerant or unresponsive to first-line therapies. As 40 % of patients with psoriasis will go on to develop PsA, regular, routine screening of psoriasis patients is recommended.
While PsA does not usually have an effect on life-expectancy, it can be associated with a reduced quality of life due to pain and disability if not diagnosed and treated early.
Last update: March 2015
- Pr Bernard COMBE
- Dr Philippe GOUPILLE