Severe Mental Illness Among Adults with Atopic Eczema or Psoriasis: Population-Based Matched Cohort Studies within UK Primary Care

Abstract

Background: Existing research exploring associations between atopic eczema (AE) or psoriasis, and severe mental illness (SMI - ie, schizophrenia, bipolar disorder, other psychoses) is limited, with longitudinal evidence particularly scarce. Therefore, temporal directions of associations are unclear. We aimed to investigate associations between AE or psoriasis and incident SMI among adults.

Methods: We conducted matched cohort studies using primary care electronic health records (January 1997 to January 2020) from the UK Clinical Practice Research Datalink GOLD. We identified two cohorts: 1) adults (≥18 years) with and without AE and 2) adults with and without psoriasis. We matched (on age, sex, general practice) adults with AE or psoriasis with up to five adults without. We used Cox regression, stratified by matched set, to estimate hazard ratios (HRs) comparing incident SMI among adults with and without AE or psoriasis.

Results: We identified 1,023,232 adults with AE and 4,908,059 without, and 363,210 with psoriasis and 1,801,875 without. After adjusting for matching variables (age, sex, general practice) and potential confounders (deprivation, calendar period) both AE and psoriasis were associated with at least a 17% increased hazard of SMI (AE: HR=1.17,95% CI=1.12-1.22; psoriasis: HR=1.26,95% CI=1.18-1.35). After additionally adjusting for potential mediators (comorbidity burden, harmful alcohol use, smoking status, body mass index, and, in AE only, sleep problems and high-dose glucocorticoids), associations with SMI did not persist for AE (HR=0.98,95% CI=0.93-1.04), and were attenuated for psoriasis (HR=1.14,95% CI=1.05-1.23).

Conclusion: Our findings suggest adults with AE or psoriasis are at increased risk of SMI compared to matched comparators. After adjusting for potential mediators, associations with SMI did not persist for AE, and were attenuated for psoriasis, suggesting that the increased risk may be explained by mediating factors (eg, sleep problems). Our research highlights the importance of monitoring mental health in adults with AE or psoriasis.

Keywords: dermatology; epidemiology; psychology.

Figure 1

Diagram of cohort study design, describing the dates of cohort entry, covariate assessment, follow-up, and study exit. ^aIdentified using an algorithm where records identified within −1 year to +1 month of the index date are regarded as the best, +1 month to +1 year from the index date as second best, the nearest before −1 year from the index date as the third best, and the nearest after +1 year from the index date as the worst. Smoking status or body mass index recorded after severe mental illness diagnosis were not used.

Figure 2

Flowchart illustrating identification of participants in atopic eczema and psoriasis cohorts. *Numbers of people with and without atopic eczema or psoriasis do not sum to the total number of individuals included in each cohort. Individuals with atopic eczema or psoriasis could be included in the matched comparison cohort up until the date of their first atopic eczema or psoriasis diagnosis.

Figure 3

HRs (95% CI) for the association between atopic eczema or psoriasis severity and severe mental illness. Models fitted to adults with complete data for all variables included in each model and from valid matched sets. ^aModel implicitly adjusted for matching variables. ^bModel further adjusted for potential confounders (socioeconomic deprivation – using Carstairs index – and calendar time. ^cConfounder adjusted model additionally adjusted for potential mediators (comorbidity burden [using Charlson comorbidity index], smoking status, harmful alcohol use, body mass index, and in atopic eczema analyses only, problems with sleep and high-dose glucocorticoid use).