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Original Investigation
June 3, 2020

Association of Skin Psoriasis and Somatic Comorbidity With the Development of Psychiatric Illness in a Nationwide Swedish Study

Author Affiliations
  • 1Division of Dermatology, Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden
  • 2Quantify Research, Stockholm, Sweden
  • 3Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden
  • 4Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
  • 5Department of Clinical Sciences, Umeå University, Umeå, Sweden
JAMA Dermatol. 2020;156(7):795-804. doi:10.1001/jamadermatol.2020.1398
Key Points

Question  How are skin psoriasis and somatic comorbidity associated with the development of psychiatric illness?

Findings  Among 93 239 patients with skin psoriasis and 1 387 495 control participants in this matched case-control study, skin psoriasis and somatic comorbidity were independently associated with 1.32 and 2.09 times increased risk, respectively, of psychiatric illness onset compared with control participants without psoriasis and without somatic comorbidity. Skin psoriasis and somatic comorbidity acted additively but not synergistically.

Meaning  Proactive, holistic treatment of patients with psoriasis is recommended because treating skin symptoms alone cannot remedy the elevated risk for psychiatric comorbidity.

Abstract

Importance  Psoriasis is a complex systemic disease with skin involvement, somatic comorbidity, and psychiatric illness (PI). Although this view of psoriasis is widely accepted, potential synergies within this triad of symptoms have not been adequately investigated.

Objectives  To investigate the independent association of skin psoriasis and somatic comorbidity with the development of PI and to assess whether skin psoriasis and somatic comorbidity act synergistically to produce a risk of PI that is greater than the additive associations.

Design, Setting, and Participants  Participants were enrolled between January 2005 and December 2010, in this retrospective matched case-control study using secondary (ie, administrative), population-based registry data from Swedish patients in routine clinical care. The dates of analysis were March 2017 to December 2019. Participants were patients with skin psoriasis and control participants without psoriasis matched on age, sex, and municipality, who were all free of preexisting PI.

Exposures  Presence of skin psoriasis and somatic comorbidity (captured through the Charlson Comorbidity Index and the Elixhauser Comorbidity Index).

Main Outcomes and Measures  Risk of PI onset (composite of depression, anxiety, and suicidality) is shown using Kaplan-Meier curves stratified by the presence of skin psoriasis and somatic comorbidity. Adjusted associations of skin psoriasis and somatic comorbidity with the development of PI were analyzed using Cox proportional hazards regression models, including interactions to assess synergistic associations. The 3 components of PI were also assessed individually.

Results  A total of 93 239 patients with skin psoriasis (mean [SD] age, 54 [17] years; 47 475 men [51%]) and 1 387 495 control participants (mean [SD] age, 54 [16] years; 702 332 men [51%]) were included in the study. As expected, patients with skin psoriasis were more likely to have somatic comorbidity and PI than control participants. Compared with those without skin psoriasis or somatic comorbidity, patients with psoriasis without somatic comorbidity had a 1.32 times higher risk of PI onset (hazard ratio [HR], 1.32; 95% CI, 1.27-1.36; P < .001), whereas patients with psoriasis with somatic comorbidity had a 2.56 times higher risk of PI onset (HR, 2.56; 95% CI, 2.46-2.66; P < .001). No synergistic associations of skin psoriasis and somatic comorbidity with the development of PI were found (HR, 0.93; 95% CI, 0.81-1.04; P = .21).

Conclusions and Relevance  This study found that somatic comorbidity appeared to alter PI onset even more than skin psoriasis. The observed association of skin psoriasis and somatic comorbidity with the development of PI reinforces the need for proactive, holistic treatment of patients with psoriasis.

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