Psoriatic arthritis is a joint disease that occurs in up to 30% of patients with psoriasis. It affects males and females in a 1:1 proportion. It can lead to permanent joint damage, causing impaired function and reducing quality of life.
Psoriasis usually manifests itself on the skin 10 years before affecting the joints, although 15% of patients may have simultaneous skin and joint manifestations or arthritis that precedes the skin lesions.
The characteristic lesions of skin psoriasis are itchy and sometimes painful raised red patches covered by a white or somewhat silvery layer of desquamation. Most common affected areas include the scalp, knees, elbows and lower back.
The patients with arthritis, in addition to the skin changes may present with different patterns of arthritis. It may be oligoarticular or polyarticular, symmetric or asymmetric involve distal joints of hands and feet but can also affect the spine. Patients may also have enthesitis (most commonly in the plantar tendons) and dactylitis (“sausage fingers or toes”).
Patients can complain of pain and stiffness in the joints that improve with activity.
The disease may be divided in these sub types:
Oligoarticular (<=4 joints, asymmetric)
Polyarticular (5 or more joints, can be symmetric and may be hard to differentiate from rheumatoid)
Distal (affects interphalangeal joints of hands and feet – including DIP, may have associated onycholysis or nail pits)
Arthritis mutilans (deforming subtype due to bone resorption or osteolysis)
The diagnosis is clinical (patient with psoriasis and an arthritis pattern compatible with psoriatic arthritis) and it may be assisted by imaging features. The Classification Criteria for Psoriatic Arthritis (CASPAR) may help:
A CASPAR Score of at least three points has a sensitivity of 91.4% and specificity of 98.7%.
Radiographs of the affected joints may show evidence of bone loss, erosion, joint-space narrowing, new bone formation, periostitis and enthesophytes. MRI may reveal erosions, synovitis and bone marrow edema.
HLA B27 can be positive in approximately 25% of the cases. ESR or C-reactive protein can be elevated in up to 40% of the cases.
The treatment should involve a team: the rheumatologist, the primary care physician and the dermatologist if needed.
Since psoriatic arthritis is a part of a bigger disease (psoriasis), when treating the patient it is relevant to know what kind of component or domain is predominant: skin lesions, peripheral joint disease, axial disease, enthesitis and/or dactylitis. Some medications may work better for a particular domain compared to others.
The goal of treatment is complete remission or minimal disease activity. In general if these goals are not reached after 3-6 months the treatment strategy should be changed.
Most patients with mild disease can benefit from NSAIDs (such as naproxen 500mg BID) with or without glucocorticoid injections. Patients with mild disease can also benefit from apremilast (PDE4 inhibitor).
Patients with moderate to severe arthritis or those resistant to NSAIDs may benefit from DMARDs such as methotrexate (15-25mg PO qWeek) or leflunomide (20mg PO daily).
Predominantly axial disease, enthesitis or severe disease (multiple joints with erosion) may be treated with anti-TNF agents since the beginning. Infliximab, adalimumab, golimumab, certolizumab and etanercept are some of the agents.
Patients that do not respond to one anti-TNF may be switched to another anti-TNF.
Patients that fail anti-TNF two times may use newer agents such as anti-IL 17 agents (ixekizumab or secukimumab ) or anti-IL12-IL23 (ustekimumab).
SOURCES & FURTHER READING:
- Ritchlin CT et al. Psoriatic Arthritis. N Engl J Med 2017; 376:957-970.
- Gossec L et al. European League Against Rheumatism recommendations for the management of psoriatic arthritis with pharmacological therapies. Annals of the Rheumatic Diseases. 2012 Volume 71, Issue 1.
- Menter A et al. Guidelines of care for the management of psoriasis and psoriatic arthritis. Journal of the American Academy of Dermatology May 2008Volume 58, Issue 5, Pages 826–850.
- Taylor, W., Gladman, D., Helliwell, P., Marchesoni, A., Mease, P. and Mielants, H. (2006), Classification criteria for psoriatic arthritis: Development of new criteria from a large international study. Arthritis & Rheumatism, 54: 2665–2673. doi:10.1002/art.21972
- Tillett W et al. The ClASsification for Psoriatic ARthritis (CASPAR) Criteria – A Retrospective Feasibility, Sensitivity, and Specificity Study. The Journal of Rheumatology January 2012, 39 (1) 154-156; DOI: https://doi.org/10.3899/jrheum.110845