Results
A total of 1,690,214 KPSC patients were eligible for the study; 10,307 (0.6%) met diagnostic and inclusion criteria for the psoriasis cohort. Patients with psoriasis had a significantly higher mean BMI (29.9 vs 28.7; P<.0001) as well as higher mean rates of alcohol use (56% vs 53%; P<.0001) and smoking (47% vs 38%; P<.01) compared to controls. Psoriasis patients had a shorter average duration of membership within the Kaiser network (P=.0001) compared to controls.
A total of 7416 patients met criteria for mild psoriasis and 2891 patients met criteria for severe psoriasis (eTable). Patients with severe psoriasis were significantly younger and had significantly higher mean BMI compared to patients with mild psoriasis (P<.0001 and P=.0001, respectively). No significant difference in rates of alcohol or tobacco use was detected among patients with mild and severe psoriasis.
Appendicitis
The prevalence of appendicitis was not significantly different between patients with and without psoriasis or between patients with mild and severe psoriasis, though the incidence rate was slightly higher among patients with psoriasis (0.80 per 1000 patient-years compared to 0.62 per 1000 patient-years among patients without psoriasis)(Table 1). However, there was not a significant difference in risk for appendicitis between healthy patients, patients with severe psoriasis, and patients with mild psoriasis after adjusting for potential confounding factors (Table 2). Interestingly, patients with severe psoriasis who had a diagnosis of appendicitis had a significantly shorter time to diagnosis of appendicitis compared to patients with mild psoriasis (7.4 years vs 8.1 years; P<.0001).
Cholecystitis
Psoriasis patients also did not have an increased prevalence of cholecystitis compared to healthy patients. However, patients with severe psoriasis had a significantly higher prevalence of cholecystitis compared to patients with mild psoriasis (P=.0038). Overall, patients with psoriasis had a slightly higher incidence rate (1.72 per 1000 patient-years) compared to healthy patients (1.46 per 1000 patient-years). Moreover, the time to diagnosis of cholecystitis was significantly shorter for patients with severe psoriasis than for patients with mild psoriasis (7.4 years vs 8.1 years; P<.0001). Mild psoriasis was associated with a significantly increased risk (HR, 1.33; 95% CI, 1.09-1.63; P<.01) for cholecystitis compared to individuals without psoriasis in both the crude and adjusted models (Table 2). There was no difference between mild psoriasis patients and severe psoriasis patients in risk for cholecystitis.
Diverticulitis
Patients with psoriasis had a significantly greater prevalence of diverticulitis compared to the control cohort (5.1% vs 4.2%; P<.0001). There was no difference in prevalence between the severe psoriasis group and the mild psoriasis group (P=.96), but the time to diagnosis of diverticulitis was shorter in the severe psoriasis group than in the mild psoriasis group (7.2 years vs 7.9 years; P<.0001). Psoriasis patients had an incidence rate of diverticulitis of 6.61 per 1000 patient-years compared to 5.38 per 1000 patient-years in the control group. Psoriasis conferred a higher risk for diverticulitis in both the crude and adjusted models (HR, 1.23; 95% CI, 1.11-1.35 [P<.001] and HR, 1.16; 95% CI, 1.05-1.29; [P<.01], respectively)(Table 3); however, when stratified by disease severity, only patients with severe psoriasis were found to be at higher risk (HR, 1.26; 95% CI, 1.15-1.61; P<.001 for the adjusted model).
