Master's Thesis Defense: Stefán Már Thorarensen

Stefán Már Thorarensen defends his master's thesis in Public Health Sciences from the Faculty of Medicine.

''Physical Trauma Increases the Incident Risk of Psoriatic Arthritis Among Psoriasis Patients: A Prospective Cohort Study''

Examiner is Helgi Jónsson, professor and specialist in rheumatology.

Supervisor is Þorvarður Jón Löve, associate professor, Faculty of Medicine, UI. Advisor is Arna Hauksdóttir, professor, Faculty of Medicine, UI. Also on the thesis committee is Sigurður Yngvi Kristinsson, professor, Faculty of Medicine, UI.

The defense is open to the public.

Abstract:

Psoriasis is a common autoimmune skin disorder. Up to one-third of psoriasis patients go on to develop the related and aptly named arthritis, psoriatic arthritis (PsA). Compared to psoriasis alone, PsA
comorbidity adds considerably to the disease burden of these patients. In the overwhelming majority of cases, psoriasis precedes PsA onset by an average of 10 years. Should a risk profile for psoriatic arthritis emerge, clinicians would be able to identify patients most likely to benefit from intervention well before
disease onset. Previous studies have identified physical trauma as a possible precipitating risk factor. However, the studies performed to date rely predominately on retrospective data and are limited in
sample size. Therefore, the aim of this thesis is to evaluate the incident risk of PsA among psoriasis patients exposed to physical trauma in a large-scale prospective cohort study generalizable to the underlying population.
A matched cohort study was performed using data from The Health Improvement Network (THIN). Psoriasis patients exposed to trauma were randomly matched to up to five unexposed psoriasis controls based on gender, age, duration of psoriasis, and entry into the database. Trauma exposure was stratified into subgroups of joint, bone, nerve, and skin trauma. Cox proportional hazards estimated the HRs for developing PsA. For comparison, an identical analysis was performed in the entire THIN population evaluating rheumatoid arthritis (RA) risk following physical trauma. The results of the study yielded 15,416 psoriasis patients exposed to trauma and 55,230 unexposed controls which were followed for a total of 425,120 person-years, during which 1010 incident cases of PsA were observed. Adjusting for potential confounders, psoriasis patients exposed to trauma had an increased risk of PsA
compared to controls, with a multivariate HR of 1.32 (95% CI 1.13 to 1.54). In our subset analysis, bone and joint trauma were associated with multivariate HRs of 1.46 (95% CI 1.04 to 2.04) and 1.5 (95% CI 1.19 to 1.90), respectively, while nerve and skin trauma were not associated with a statistically significant increase in risk compared to controls. Finally, patients exposed to trauma in the entire THIN population did not have an increased risk of developing RA: HR 1.04 (95% CI 0.99 to 1.10).

In summary, this study finds an increased risk of developing PsA among psoriasis patients exposed to physical trauma. As the literature concerning PsA risk factors grows, clinicians will be better able to identify and treat high-risk patients earlier, thus improving outcomes.