Original article
The burden of autoimmune disease: A comparison of prevalence ratios in patients with psoriatic arthritis and psoriasis

https://doi.org/10.1016/j.jaad.2009.02.015Get rights and content

Background

Current research has confirmed that many inflammatory autoimmune (AI) diseases are due to derangements in multiple cytokine pathways. Some of these cytokines appear to play comparable key roles across diseases, suggesting that a similar underlying systemic inflammatory cascade could be responsible for various disease states. A recent study supports the hypothesis of a common cytokine-based pathology by showing that having one AI disease significantly increased the risk of having another AI disease. Psoriasis is an AI, manifesting as a chronic inflammatory skin condition and is clearly associated with other conditions, most obviously psoriatic arthritis (PsA).

Objective

We sought to examine whether patients with PsA enrolled in managed health care plans carry a higher AI disease burden than patients with cutaneous psoriasis only (PsO).

Methods

Patients 18 years or older enrolled in a health claims database were classified by two clinical subtypes: PsA and PsO. Control subjects were matched 3:1 to patients with psoriasis on age, sex, census region, and length of previous medical insurance coverage. AI disease diagnoses were identified through International Classification of Diseases, Ninth Revision codes. The association of other AI diseases with each psoriasis cohort was assessed using a prevalence ratio.

Results

PsO was associated with a higher prevalence ratio for the 3 gastrointestinal diseases: Crohn disease (1.6 [confidence interval {CI} 1.4-2.0]), ulcerative colitis (1.3 [CI 1.1-1.6]), and inflammatory bowel disease (1.4 [CI 1.2-1.6]). PsA was also associated with a higher prevalence ratio for the gastrointestinal diseases: Crohn disease (2.1 [CI 1.3-3.3]), ulcerative colitis (2.0 [CI 1.3-3.1]), and inflammatory bowel disease (1.8 [CI 1.3-2.5]). Patients with PsA had an increased prevalence ratio associated with giant cell arteritis (4.8 [CI 1.5-15.7]) and pulmonary fibrosis (1.9 [CI 1.2-3.0]).

Limitations

Detection and misclassification biases may have affected these findings.

Conclusions

These findings support the hypothesis that PsA and PsO are associated with development of other AI diseases. The data suggest that evaluating patients with psoriasis for other associated disorders in a prospective manner may be important, because they may be more likely to experience the onset of another AI disease. Treatment planning for these patients could, therefore, require the medical management of more than one AI disease. Further, our data suggest that PsA and PsO may be divergent in ways previously not described that could inform future research.

Section snippets

Methods

The methods used in this study have been described elsewhere by Robinson et al.5 Patients were chosen who were 18 years or older in 2001 and continuously enrolled from 2001 to 2002 in the IMS Health Integrated Administrative Claims Database (Norwalk, CT). During this period the database contained an initial population of approximately 11 million covered lives. Patients who had at least one medical service visit of any kind between January 1, 2001, and December 31, 2002, were identified. Those

Results

The prevalence for the overall psoriasis population was 0.89% with 12% of that population being the PsA subtype. No meaningful difference was found in sex distribution across the populations (51% for all) or in regional distribution. Patients with PsA were approximately 2 years older. The matching process produced very well-balanced control subjects by all criteria, including length of previous medical coverage (Table II).

Patients with PsO had an increased PR associated with all the

Discussion

This retrospective cohort study using US health care claims data generates important hypotheses about the nature and level of association between patients with psoriasis and AI disease. In the largest dataset we have looked at to answer this question, different relationships were found among patients with PsA, their counterparts with cutaneous PsO, and the AI diseases of this study. When statistically significant trends were found between several AI diseases and both psoriasis subtypes, the

Limitations

There are several important limitations in this study. This study used a prevalence-based design, making disease duration a confounding factor when interpreting results. Furthermore, health care claims data in the United States have many constraints when used for epidemiologic research; perhaps the most significant is the strong interrelationship among case identification, disease severity, payment policy, and treatment setting. The accuracy of the diagnosis codes attached to the medical claims

Conclusions

There are 3 important results from this study. The first is that these findings support the hypothesis that PsA and PsO are associated with development of other AI diseases. Second, our data suggest that evaluating patients for other associated disorders in a prospective manner may be important. Because our data suggest that patients with PsA have a higher AI disease burden than patients with PsO, monitoring these patients for the onset of other AI diseases may be warranted as part of their

References (25)

  • A.B. Kimball et al.

    Cardiovascular disease and risk factors among psoriasis patients in two US healthcare databases, 2001-2002

    Dermatology

    (2008)
  • Y. Wu et al.

    Psoriasis: cardiovascular risk factors and other disease comorbidities

    J Drugs Dermatol

    (2008)
  • Cited by (90)

    View all citing articles on Scopus

    Data acquisition was supported by Centocor.

    Disclosure: Mr Robinson is an employee and stockholder of Johnson & Johnson. Dr Bala is a stockholder of Johnson & Johnson and an employee of Glaxo Smith Kline. Dr Kimball has been an investigator, speaker, and consultant for Abbott, Centocor, and Amgen. Dr Makredes has no conflicts of interest to declare.

    Presented in part in poster format at the Society of Investigative Dermatology Annual Meeting in Kyoto, Japan, May 14-18, 2008.

    View full text