Psoriatic arthritis (PA) is a specific type of arthritis that has been diagnosed in approximately 23% of those who have psoriasis.
PA can occur in any age group; however, in most patients, it manifests itself between 30 and 50 years of age. On average, PA appears about 10 years after the first signs of psoriasis occur, but in about 1 of 7 people with PA, arthritis symptoms occur before any skin lesions appear. Most patients with PA also have psoriasis; patients rarely have PA without psoriasis.
A haplotype epidemiologic association with PA involves the expression of both class I and class II human leukocyte antigen (HLA) alleles, including HLA-B13, HLA-B17, HLA-B27, HLA-B38, HLA-B39, HLA-Cw6, HLA-DR4, and HLA-DR7. HLA-B27 is present in 60% of individuals with the disease, as compared with 8% of the general population.
Dactylitis, which is associated with more erosive forms of PA, is often the initial feature of PA and may be the only feature for months to years.
Guidelines on psoriatic arthritis have been published by organizations such as the American College of Rheumatology/National Psoriasis Foundation, European League Against Rheumatism (EULAR), the British Society of Rheumatology (BSR), and the American Academy of Dermatology (AAD).
Types of PA
Five types of PA have been defined; these types can coexist, but they tend to occur separately in most cases:
Arthritis involving primarily the small joints of the fingers or toes (asymmetrical oligoarthritis) — 55-70%
Asymmetrical arthritis, which involves the joints of the extremities — 30-50%
Symmetrical polyarthritis, which resembles RA — 15-70%
Arthritis mutilans, which is a rare but deforming and destructive condition — 3-5%
Arthritis of the sacroiliac joints and spine (psoriatic spondylitis) — 5-33%.
PA is diagnosed and assessed with radiography, which is the cornerstone in assessing and monitoring inflammatory arthritides such as PA. Radiographic findings are reproducible and allow for the serial monitoring of patients. Although magnetic resonance imaging (MRI) is more sensitive, the cost of this modality makes it a second-line means for monitoring patients with PA.
Ultrasound has played a role because of its lack of radiation exposure and easy accessibility. This technique is more sensitive and specific than clinical examination in detecting active synovitis, and the identification of specific synovitis patterns enables differentiation of PA from RA and other entities.
The Andersson lesion (erosive discovertebral lesion) can be the initial sign of pathology in axial PA.
Early recognition and treatment are likely to result in better long-term outcomes. Delay in diagnoses of 6 and 12 months have been shown to impact on long-term joint damage and functional disability.
Factors that portend a worse prognosis for patients with PA include the following:
A strong family history of psoriasis
Disease onset younger than age 20 years
Expression of HLA-B27, HLA-Cw6, or HLA-DR4 alleles
Extensive skin involvement
In addition, 40% of PA patients fulfill the diagnosis for metabolic syndrome, which contributes to an increased cardiovascular risk. Effective management of metabolic syndrome is key to minimizing morbidity and mortality.
Differential diagnosis includes ankylosing spondylitis and rheumatoid arthritis of the hands and spine. Enteropathic arthritis (arthritis of inflammatory bowel disease) should also be considered, and spotted bone disease has been reported in a patient with psoriatic arthritis.
For patient education resources, see the Skin Conditions & Beauty Center, as well as Types of Psoriasis, Psoriatic Arthritis, and Psoriasis Medications.