Dear Editor, Psoriasis is present in 2–3% of the adult European population1 and in 0·7–1·2% of children.1,2 Adults with psoriasis have increased risk of depression,3 and U.S. data reported an increased risk of psychiatric diseases in paediatric patients with psoriasis;4 however, European data are lacking. The primary aim of the current study was to examine the risk of psychiatric disorders including use of psychopharmacotherapy in children with psoriasis compared with healthy controls in a population‐based cohort study. In Denmark, complete data on diagnoses [International Classification of Disease (ICD) codes], medication use [Anatomical Therapeutic Chemical (ATC) codes] and statistics can be linked at an individual level in nationwide registers.5 Patients were classified with psoriasis by diagnosis or pharmacotherapy as described previously.6 We identified patients with psoriasis aged < 18 years between January 1997 and December 2012. We defined the index date as the time of the first psoriasis diagnosis. Each patient was matched (for age, sex and calendar time) with 10 controls without psoriasis. The index date for controls was defined as the date of first psoriasis diagnosis for the corresponding case. The cohort was followed until migration, death or the occurrence of an end point, whichever came first. We excluded patients with a history of mental disorders (ICD‐8 codes 290–315; ICD‐10 code group F) or drug use for treatment of mental disorders (ATC code groups N05–N07) prior to the start of the study. We examined the association between psoriasis and alcohol abuse, anxiety disorders (ICD‐10 F40–F42), depression (ICD‐10 F32–F33), eating disorders (ICD‐10 F50), initiation of antidepressants (ATC N06A), initiation of antipsychotics (ATC N05A), drug abuse (F11–F19) and use of benzodiazepine derivatives (ATC N05CD). Collection of data on alcohol abuse was performed as previously described.7 End points were decided a priori. We described baseline characteristics with means and SDs for continuous variables and frequencies and percentages for categorical variables. Incidence rates were summarized per 1000 person‐years. Cox proportional hazards models were used to estimate crude and adjusted (age, sex and diabetes) hazard ratios (HRs). Due to its association with psoriasis, adjustment for diabetes was performed. The proportional hazards assumption, interactions and linearity of continuous variables were tested and found valid. Analyses were performed using SAS 9.4 (SAS Institute Inc., Cary, NC, U.S.A.) and Stata 11.2 (StataCorp, College Station, TX, U.S.A.). The study population included 4410 patients with psoriasis and 41 285 matched controls (Table 1). In the psoriasis cohort 59·2% were female. The mean follow‐up time was 7·1 ± 4·6 years for controls and 7·1 ± 4·7 years for patients with psoriasis. Baseline characteristics of the study population Values are n (%) unless stated otherwise. Baseline characteristics of the study population Values are n (%) unless stated otherwise. Incidence rates were generally higher for all measured outcomes among patients with psoriasis vs. controls (Table 2). In patients with psoriasis, adjusted analyses showed increased risk of alcohol abuse [adjusted HR 1·42, 95% confidence interval (CI) 1·14–1·76], depression (adjusted HR 1·94, 95% CI 1·27–2·96) and eating disorders (adjusted HR 2·03, 95% CI 1·20–3·43). However, there was no significant difference between the groups regarding the risk of anxiety (adjusted HR 1·44, 95% CI 0·89–2·34; P =0·14), but there was a 3·5‐fold increased risk of benzodiazepine use (adjusted HR 3·57, 95% CI 2·13–5·97) in patients with psoriasis vs. controls. Similarly, in patients with psoriasis, there was a significantly increased risk of antidepressant use (adjusted HR 1·61, 95% CI 1·44–1·79), use of antipsychotics (adjusted HR 1·35, 95% CI 1·10–1·68) and risk of drug abuse (adjusted HR 1·51, 95% CI 1·04–2·19) compared with controls. Summary of number of events, follow‐up time, incidence rates per 1000 person‐years, and crude and adjusted hazard ratios (HRs) of the associations between psoriasis and the respective outcomes IR, incidence rate; CI, confidence interval. aAdjusted for age, sex and diabetes. Summary of number of events, follow‐up time, incidence rates per 1000 person‐years, and crude and adjusted hazard ratios (HRs) of the associations between psoriasis and the respective outcomes IR, incidence rate; CI, confidence interval. aAdjusted for age, sex and diabetes. To our knowledge, this is the first large‐scale European study to evaluate the risk of psychiatric disorders and use of psychopharmacotherapy in paediatric patients with psoriasis. Our data suggest that patients with psoriasis may be at high risk for psychiatric diagnosis and treatment of psychiatric disorders. An explanation may be social stigmatization caused by psoriasis resulting in behavioural changes. Moreover, depression may lead to increased risk behaviour. Indeed, studies have reported a higher frequency of alcohol abuse in adults with psoriasis.8,9 It is worth noting that we did not find a positive association between anxiety and psoriasis, but there was a twofold increased risk of eating disorders in these patients. Recently, Kimball et al. conducted a study in the U.S.A. and found a 23% increased risk of depression in paediatric patients with psoriasis, and overall our findings are in agreement with the observations made by Kimball and others.3,4 Strengths of this study include the large sample size and use of nationwide register data, lowering the risk of recall bias, and equally accessible health care to all patients, which minimized selection bias. However, the Danish registries do not contain information on possible confounders such as socioeconomic status and obesity. Moreover, we lacked information on psoriasis severity and benzodiazepine indication. Also, patients with mild symptoms may have been treated at their general practitioner with therapy only, leading to unregistered cases, although in Denmark it is common for children with psychiatric disorders to be treated in hospital. Furthermore, patients treated with steroids only could have caused misclassification of cases, thus the true numbers may be even higher. Risk of detection bias cannot be excluded, as patients with psoriasis are more likely to have contact with hospitals, leading to increased focus on symptoms, potentially resulting in psychopharmacotherapy prescription. In conclusion, psoriasis in children confers a significant psychosocial disease burden, with an increased risk of several psychiatric disorders and treatment for psychiatric diseases. Conflicts of interest: T.T. has served as investigator for Novartis and LEO Pharma. A.E. has received research funding and/or consultancy honoraria from Pfizer and Eli Lilly. G.G. is supported by an unrestricted research scholarship from the Novo Nordisk Foundation and reports research grants from Pfizer, Bristol‐Myers Squibb, AstraZeneca, Bayer and Boehringer Ingelheim. L.S. has received consultancy and/or speaker honoraria from AbbVie, Pfizer, Janssen‐Cilag, Merck Sharp & Dohme and LEO Pharma and is a member of the advisory boards of AbbVie, Pfizer, Janssen‐Cilag, Merck Sharp & Dohme, Eli Lilly, Celgene and Novartis.
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Todberg et al. (2016) studied this question.
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