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Hidradenitis Suppurativa And Psoriasis

Hidradenitis suppurativa (HS) is a chronic, debilitating, and inflammatory skin disease. The epidemiology of HS varies greatly, with an estimated prevalence ranging from 0.03% to 4% worldwide. Similar to psoriasis (PsO), HS also exhibits a systemic inflammatory nature with a spectrum of systemic comorbidities. A large health insurance claims (HICs) database is analyzed to determine the demography and epidemiology of HS, PsO, and HS with concurrent PsO (HS-PsO) patients. Furthermore, the comorbidity profiles, including the comorbidity risk of these patient populations, are analyzed.

Methods

This is a noninterventional retrospective analysis of anonymized HICs data using a subset of the Institute of Applied Health Research Berlin (InGef) database. The primary outcome is the prevalence and incidence of HS, PsO, and HS-PsO. Secondary outcomes include comorbidity profiles and a comorbidity risk analysis.

Results

The prevalence and incidence of HS were 0.0681% and 0.0101%, respectively. The prevalence of HS-PsO was 0.004% (6% of the total HS population). HS patients frequently suffered from arterial hypertension (45%), nicotine dependence (46%), obesity (41%), and depression (36%), which were more common in HS-PsO patients compared with HS alone. HS patients had an increased prevalence of metabolic, psychiatric, immune-mediated, and cardiovascular diseases, e.g., overweight/obesity [odds ratio (OR): 2.65, 95% confidence interval (CI) 2.37–2.96], depression (OR: 1.55, 95% CI 1.42–1.76), or seronegative rheumatoid arthritis (OR: 2.82, 95% CI 1.61–4.94) compared with the overall population. The increased risk of myocardial infarction in HS patients (OR: 4.1, 95% CI 3.5–4.8, adjusting for age/sex) was largely attributed to patient’s current smoking status (OR: 1.1, 95% CI 0.8–1.5, adjusting for smoking/age/sex).

Conclusions

HS patients show a broad spectrum of inflammatory and metabolic syndrome-related comorbidities, with an increased risk by concurrent PsO. Important for clinical practice, the elevated cardiovascular risk of HS patients can be largely attributed to smoking.

Key Summary Points

A health insurance dataset of more than 7 million individuals in Germany was analyzed to determine the epidemiology, comorbidity profiles, and comorbidity risk of hidradenitis suppurativa (HS), psoriasis (PsO), and HS with concomitant PsO.
The prevalence and incidence of HS was 68/100,000 and 10.1/100,000; Approximately 6% of HS patients had a concomitant diagnosis of PsO.
HS patients showed an increased risk for metabolic, psychiatric, immune-mediated, and cardiovascular comorbidities.
HS with concomitant PsO aggravated comorbidity frequencies of HS patients, especially regarding psychiatric diseases.
The increased risk to develop cardiovascular comorbidities in HS patients was largely attributed to smoking.

Introduction

Hidradenitis suppurativa (HS) is a chronic, progressive, highly inflammatory, painful, and destructive follicular skin disorder. HS manifests in nodules which can progress to abscesses, sinus tracts, and fistulae [1]. Inflammatory lesions mainly affect the inverse body areas, including axillae, the inguinal and anogenital region, and inframammary areas in women [23]. Women are more frequently affected than men, with a ratio of 3:1 [45]. Due to variations in clinical appearance, treatment response, and involved specialties, accurate diagnosis can be complex and is often delayed [6].

Conflicting opinions exist regarding the epidemiology of HS, with an estimated prevalence ranging from 0.03% to 4% worldwide [78]. The average prevalence has been reported as 0.8% in the UK [9], 1% in France, 0.7% in Australia [10], and 0.1% in the USA [11]. Scarce data on global incidences of HS are available; a study from the UK reported an annual incidence of physician-diagnosed cases from 1996 to 2013 as 0.028% [9]; however, in the USA, an overall incidence of 0.011% was reported between 2015 and 2016 [11].

In comparison with other chronic cutaneous diseases such as psoriasis (PsO), expenses for HS disease management are dominated by high-cost settings, e.g., inpatient and emergency department care, including surgical interventions [12]. In addition to the severe impact on a patient’s quality of life (QoL), HS impairs the patient’s ability to work, subsequently affecting annual income, resulting in both unmet medical and socioeconomic needs [1314].

To provide optimal health care to HS patients and to quantify the societal burden of this disease, it is essential to understand the demography and epidemiology of HS, frequently associated comorbidities, and risk factors. Analysis of the comorbidity profile and risk are important to understand and dissect the systemic aspects of the disease and can help to optimize clinical care.

Smoking has been attributed to HS development and has been identified as a decisive risk factor, with the incidence of HS doubled amongst smokers compared with nonsmokers [51516]. HS is often accompanied by severe comorbidities, including metabolic syndrome and Crohn’s disease (CD) [617]. In addition, patients with HS have a higher prevalence of depression, anxiety, and suicidal ideation, demonstrating the impact of HS on psychosocial wellbeing and QoL [1819].

HS and PsO have overlapping immunopathogenic pathways as well as patterns of inflammation-related comorbidity [20]. Data on co-occurrence of both pathologies are however scarce. Type 1 and 3 cytokines such as TNF-α, Interferon-γ, IL-1-α/β, IL-6, IL-8, and IL-17 are upregulated, indicating that the Th1/Th17 axis is activated and may drive inflammation in both diseases [2122].

A large-scale population study in Israel reported a greater prevalence of HS in PsO patients than in the general population. HS and PsO coexistence was associated with an increased prevalence of obesity and smoking [23]. A Danish monocentric analysis of patients with HS and PsO consistently observed a threefold increased risk of HS patients for concomitant PsO [24]; other studies suggest more severe comorbidities in concomitant HS and PsO [25].

The present study is conducted to assess the demography and epidemiology of HS patients, PsO patients, and HS patients with concurrent PsO in the German population. In addition, comorbidity profiles are assessed, and a risk analysis is conducted for metabolic, cardiovascular, psychiatric, and immunological comorbidities.

Methods

Study Design and Data Source

Approximately 85% of the German population (~ 70 million individuals) are insured by the statutory health insurance (SHI) system, which includes approximately 120 independent health insurance companies. This is a noninterventional retrospective analysis conducted using health insurance claims (HICs) data from the Forschungsdatenbank des InGef – Institut für angewandte Versorgungsforschung Berlin GmbH (InGef) research database. InGef is a complete longitudinal claims dataset of approximately 7 million individual patients. InGef includes data from different health care sectors ranging from outpatient care, hospital treatment, and the pharmacy sector to data about physiotherapy and technical aids. The analyses were completed on a subset of 4.1 million patients stratified by age and sex based on the population structure of Germany in 2013 (German Federal Statistical Office DeStatis), which allows extrapolation of these epidemiological findings to the overall German adult population.

All patient-level data in the InGef research database were deidentified to comply with data protection regulations. Use of the study database for health services research is therefore fully compliant with German federal law, and accordingly, ethical approval was not needed.

Study Population

The observational period spanned from January 1, 2012 to December 31, 2017. Adult patients (≥ 18 years) who were continually insured without interruption within the above time frame and with a diagnosis of HS and/or PsO were included in this study. Diagnosis could be a hospital main secondary discharge or outpatient diagnosis verified in at least two quarters within one rolling year (M2Q criterion). Patients with HS and PsO were identified using the International Statistical Classification of Diseases and Related Health Problems (ICD) codes (10th revision, German modification; L73.2: hidradenitis suppurativa, L40.0: plaque psoriasis).

Epidemiological Measures

HS prevalence was classified as having a documented HS diagnosis (M2Q) between January 1, 2012 and December 31, 2016. Similarly, PsO prevalence was classified as having a diagnosis of PsO with no concomitant HS (M2Q) in the same time period. Prevalence of HS with concurrent PsO (HS-PsO) was classified as having a diagnosis of HS and PsO (M2Q) between January 1, 2012 and December 31, 2016. Incidence of either HS, PsO, or HS-PsO was defined by a diagnosis of HS, PsO, or HS-PsO between January 1, 2017 and December 31, 2017 with no prior diagnosis of HS, PsO, or HS-PsO, respectively, between January 1, 2012 and December 31, 2016. The incidence and prevalence of HS, PsO, and HS-PsO were calculated by dividing the total number of diagnosed patients by the total number of adults in the database within the specified period.

Patient Characteristics and Comorbidity Profiles

Secondary objectives of this study include examining patient demographics (age and sex), diagnosing specialties, comorbidity profiles (frequently documented diagnoses on ICD-10 GM three-digit level relevant to HS), and risk of comorbidity development.

Comorbidities were grouped into four main categories: metabolic, psychiatric, cardiovascular, and autoimmune/immune related. The frequency of comorbidities in HS, PsO, and HS-PsO were compared with a reference population insured by the SHI system in Germany. To analyze the comorbidity risk, HS, PsO, and HS-PsO patients were age and sex matched to the SHI German population at a ratio of 1:4. For each patient of each target population, four individuals both age and sex matched with no diagnosis of PsO or HS were selected from the database of SHI individuals as healthy controls (control population). Analogous to the patient cohort, only patients who were continually insured from January 1, 2012 to December 31, 2017 and ≥ 18 years were included. As smoking is highly prevalent among HS patients and can have an impact on certain comorbidities, risk analysis was carried out in matched as well as unmatched for tobacco abuse/nicotine dependence (smoking status) [1626]. This enabled the assessment of the impact of smoking on comorbidity risk. Parameters calculated include the odds-ratio (OR), 95% confidence interval (CI), and p-values for each individual comorbidity compared with the SHI German population.

Data Analysis

SAS Enterprise Guide software (version 9.2) was used for statistical programming. All HS and PsO patients fulfilling the inclusion criteria were included in the analyses to get representative results for the German population. The estimation of the overall SHI German population was based on the official statistics of individuals covered by SHI in the respective year (https://www.gbe-bund.de). The ratio of insured individuals in the official statistics to patients found in the age and sex stratified analytical database was used as a factor to extrapolate the total number of individuals under SHI coverage. This factor was derived from the following formula:

{\text{Extrapolation}}\;{\text{Factor}} = \frac{{N_{{{\text{SHI}}}} }}{{N_{{{\text{Database}}}} }},

where NSHI represents the total number of individuals enrolled in SHI and NDatabase represents the total number of individuals in the research database.

A factor of 20.16 was used to extrapolate results to the SHI population.