The Epidemiology of Psoriatic Arthritis

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Key points

  • Psoriatic arthritis (PsA) is a clinically heterogeneous inflammatory arthritis that is common among patients with psoriasis.

  • PsA remains underdiagnosed.

  • Early identification of PsA is important in order to improve long-term outcomes.

  • Knowledge of risk factors for PsA and use of screening tools may improve recognition of PsA among patients with psoriasis.

Methods

The authors performed a systematic review by combining “psoriasis or psoriatic arthritis” with the following MeSH terms: epidemiology, classification, diagnosis, complications, mortality in Ovid Medline. This review resulted in 8936 citations. After limiting to English papers, humans, and 2006 to current, 3515 citations remained. Titles and abstracts were reviewed for these remaining papers. Papers were excluded if they did not refer to psoriasis or PsA (N = 288), were case reports (N = 644),

Prevalence and incidence of psoriatic arthritis in the population

Several studies have examined the prevalence of PsA in countries all over the world. Prevalence estimates in the United States range from 0.06% to 0.25% with the lowest estimate derived from a paper that used International Classification of Disease, ninth edition (ICD-9), codes to identify cases and the highest from articles using patient self-report of diagnosis of PsA.4, 5, 6 Prevalence estimates in Europe range from 0.05% in Turkey7 and the Czech Republic8 to 0.21% in Sweden.9, 10, 11, 12

Prevalence and incidence of psoriatic arthritis among patients with psoriasis

Although PsA has a low prevalence in the general population, it is common among patients with psoriasis. Again, prevalence estimates vary considerably (range 6%–41%) depending on the definitions used (ie, diagnostic codes, rheumatologist diagnosis, classification criteria, diagnostic codes, and the populations measured).10, 11, 14, 15, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 Wilson and colleagues examined the cumulative incidence of PsA over time in patients with psoriasis and reported 1.7%,

Alternative diagnoses, missed diagnoses, and misclassification in studies of psoriatic arthritis

Studying the epidemiology of PsA is challenging given the absence of definitive, gold-standard diagnostic tests for PsA and the heterogeneous manifestations of the disease. In addition, patients with psoriasis often have other common reasons for joint pain, such as osteoarthritis, gout, and fibromyalgia, which can easily be mistaken for PsA.30, 31, 32, 33, 34 When using diagnosis codes to define PsA, there is often a concern for misclassification given that patients with psoriasis could have

Defining and classifying psoriatic arthritis

Classification criteria are designed to create more homogenous populations for research.35 Several sets of classification criteria for PsA have been created since the original Moll and Wright criteria in 1973.36 These criteria include the Amor criteria, European Spondylarthropathy Study Group criteria, Vasey and Espinoza criteria, and Classification of Psoriatic Arthritis (CASPAR) criteria.3, 37, 38, 39, 40, 41, 42 There is a great deal of variability among the criteria components and test

Psoriatic arthritis is a heterogeneous disease

PsA is a clinically heterogeneous disorder. Five subtypes of psoriatic arthritis were initially defined by Moll and Wright: monoarthritis or oligoarthritis, polyarthritis, distal interphalangeal (DIP) joint predominant disease, psoriatic spondylitis or sacroiliitis, and arthritis mutilans.36 It is now recognized that patients can have any combination of the disease features: peripheral arthritis (monoarticular, oligoarticular, or polyarticular with or without DIP involvement), enthesitis,

Psoriatic arthritis in children

Psoriasis and PsA are not limited to adults. Juvenile psoriasis has a prevalence of approximately 0.7% increasing from 0.12% at age 1% to 1.2% at age 18.100, 101 Juvenile PsA (JPsA) accounts for approximately 6% to 8% of all cases of juvenile arthritis.73, 102, 103 Unlike adult PsA, inflammatory arthritis precedes skin psoriasis in about half of children with JPsA,104 often making the diagnosis and classification of JPsA quite challenging. Two sets of classification criteria for JPsA exist: the

Recognition of early psoriatic arthritis

Early PsA is generally considered within the first 2 years of symptom onset.113 Increasing evidence supports the early diagnosis and treatment of PsA in order to improve long-term outcomes.113, 114, 115, 116 Gladman and colleagues114 found patients presenting within 2 years of symptom onset had significantly less disease progression after adjusting for baseline characteristics, including start of DMARD therapy at the first visit. Treatment outcomes may also be different among patients with

Subclinical disease in patients with psoriasis

Given that early initiation of therapy may decrease joint damage and improve long-term outcomes, how early should therapy be initiated? It has long been recognized that patients may not report symptoms of joint pain or may not be aware of joint inflammation. Several studies demonstrate that patients with psoriasis often have “subclinical” joint and entheseal inflammation.120, 121 The prevalence of subclinical synovitis and enthesopathy among patients with psoriasis ranges from 3% to 46% and 7%

Improving detection of psoriatic arthritis among patients with psoriasis

How can one better identify PsA? Understanding risk factors for PsA among patients with psoriasis could help identify patients with psoriasis who are more likely to develop the disease.129 In addition, the use of screening tools for PsA in dermatology clinics could facilitate improved recognition of existing disease.

Comorbidities in psoriatic arthritis

Over the past decade, the understanding of PsA as systemic disease has significantly expanded.163 Approximately 40% of patients with PsA had 3 or more comorbid conditions, and the presence of a comorbidity was associated with decreased quality of life.164 Comorbidities reported to have an increased prevalence or incidence in PsA are reported in Box 2. The increased risk for metabolic abnormalities including cardiovascular disease and diabetes have been the most striking and of greatest

Summary

PsA is a chronic inflammatory arthritis with potentially significant functional disability and poor outcomes, including cardiovascular disease. Early detection of PsA is important for improvement in long-term outcomes. Use of screening tools and improved knowledge of risk factors could improve early detection.

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    Disclosure Statement: The authors have nothing to disclose.

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