A new study conducted by Shu-Hui Wang and colleagues looks to examine the relationship between psoriasis and uveitis.
Psoriasis and psoriatic arthritis can lead to inflammation of the eyes, a condition termed uveitis (pronounced ‘you-vee-EYE-tis”), a disorder that affects approximately one in 1000 Americans. A nationwide cohort study that examined nearly 147 954 Han Chinese individuals with psoriasis including more than 10,107 with concomitant psoriatic arthritis, 137 847 without psoriatic arthritis and 147 954 matched non-psoriatic controls found that there was a higher incidence of uveitis in individuals with psoriasis, irrespective of whether they had psoriatic arthritis, compared to the controls.
Psoriasis is a systemic and chronic disease that is mediated by an immune system gone awry in combination with various genetic and environmental factors. Psoriasis is not restricted to the skin and epidemiological studies show that psoriasis is associated with an increased risk of mortality and morbidities. Activation of T cells and consequently, that of inflammatory cells in the skin promote the proliferation of keratinocytes and epidermal hyperplasia. Pro-inflammatory cytokines released by T cells, including TNFα, IL-2 and Interferons induce an inflammatory cascade. Medications such as efalizumab and alefacept as well as anti-TNFα drugs such as infliximab, etanercept and adalimumab are used to treat and control psoriasis.
Uveitis is a condition characterized by intraocular inflammation with about 40% being secondary to an immune-mediated disease and 30% not fitting into any well-defined etiology. Development of uveitis shows genetic predisposition with a strong link between uveitis and a locus on chromosome 9. Studies show that Th17 and Th1 immune responses are involved in the immunopathogenesis of the disease, with IL-17 and TNFα levels being particularly high in the aqueous humor of patients with uveitis.
Patients with psoriasis are more likely to get uveitis than the average individual and strikingly, patients with psoriatic arthritis have a higher risk, with at least 7% developing uveitis. Very few studies have examined the ophthalmological pathologies associated with psoriasis and studies that have evaluated the association, particularly in the case of uveitis, are largely inconclusive due to contradictory findings. To put to rest such conflicts, Shu-Hui Wang and colleagues at the Far Eastern Memorial Hospital in Taiwan identified psoriatic patients from a specialized dataset that contained all people with psoriasis from 2000 to 2011 in the National Health Insurance Research Database, with controls selected from the 2005 Longitudinal Health Insurance Database that provided longitudinally linked anonymized data of 1 million enrollees. Using univariate and multivariate Cox proportional hazard models to estimate the hazard ratios and 95% confidence intervals for the association between statusof psoriasis and uveitis occurrence, the primary outcome of interest, Shu-Hui Wang and colleagues demonstrated that patients with psoriasis and psoriatic arthritis had 160.88 incidences of uveitis per 100,000 person-years, patients with psoriasis and without psoriatic arthritis had 103.99 incidences of uveitis per 100,000 person-years compared to 87.23 in the controls.
This study is at odds with another study examining a Turkish population which showed no relationship between psoriasis and uveitis. Limitations of the study include the possibility of misclassification of patients with psoriasis and psoriatic arthritis, those who were rated based on the severity of the disease, and the generalizability of the results since the population studied was Han Chinese. However, the results may serve as a guide for uveitis risk stratification among patients who present with a varied inflammatory profile and help patients to understand the risk and manifestations of uveitis.
Written By: Joseph M. Antony, PhD