Exploring disease comorbidities and temporal disease progression of psoriasis: an observational, retrospective, multi-database, cohort study

BACKGROUND: Comorbidities associated with psoriasis are well documented. However, few studies have explored the comorbidity trajectories that patients with psoriasis commonly experience over time. This study reports the 5-year comorbidity trajectories of patients with psoriasis. OBJECTIVES: To determine the long-term comorbidity trajectories of patients with psoriasis in Denmark. METHODS: This observational cohort study explored the Danish National Patient Registry (DNPR) between 1999 and 2013 to identify comorbidities diagnosed 5 years prior to or after a psoriasis diagnosis. Comorbidity occurrence in patients with psoriasis (psoriasis cohort) was compared with patients without psoriasis (the N group). Comparison groups, each the same size as the psoriasis cohort, were created by selecting random patients from the N group. If a comorbidity occurrence was higher in more than nine comparison groups than in the psoriasis cohort, it was not analysed and only comorbidities that occurred in ≥ 0·8% of the psoriasis cohort were analysed. The strength of association between a psoriasis diagnosis and a comorbidity diagnosis was measured using relative risk (RR). All psoriasis and comorbidity pairs that achieved RR > 1 (P < 0·001) (known as a Diagnosed Pair) were tested for directionality to identify the sequence of diagnoses using a binomial test. Diagnosed Pairs with a statistically significant direction (Bonferroni corrected P-value < 0·025) were then used to create comorbidity trajectory clusters 5 years before and after a psoriasis diagnosis. RESULTS: A total of 17 683 patients with psoriasis were compared with 10 000 comparison groups. A total of 121 comorbidities met the minimum criteria that ≥ 0·8% of the psoriasis cohort were diagnosed with the comorbidity within 5 years (before or after) of their psoriasis diagnosis. Thirty-eight of these comorbidities achieved RR > 1 (P < 0·001) with psoriasis, of which 19 achieved a significant direction from psoriasis to a comorbidity (including psoriasis to hypothyroidism), and four achieved a significant direction from a comorbidity diagnosis to a psoriasis diagnosis (including Crohn disease to psoriasis); four of five comorbidity trajectories with three sequential diagnoses achieved an RR > 1 (P < 0·001) and a significant direction from psoriasis to the first comorbidity to the second comorbidity (including psoriasis to hypertension to atrial fibrillation and flutter). CONCLUSIONS: Comorbidity trajectories may support clinicians in conducting disease risk analyses of patients with psoriasis and help plan optimal treatment to prevent future high-risk comorbidities.