Abstract
This cohort study examines the median age at onset of hidradenitis suppurativa and compares age at onset across sex, race, and disease severity of individuals.
Although hidradenitis suppurativa (HS) has a reported mean age at onset of 21.8 years,1 we have observed initial onset of HS lesions in individuals older than 40 years more commonly than expected. In this retrospective study, we investigated age at HS onset and its distribution.
Methods
With ethics board approval from all participating institutions, deidentified data from the medical records of 1203 patients with dermatologist-confirmed cases of HS from 3 North American HS practices were aggregated. Collected data included age at visit, sex, race, self-identified ethnicity, self-reported age at HS onset, and disease severity by Hurley stage. All analyses were conducted using R software, version 3.5.0. Wilcoxon tests were used to compare age at onset across sex, race, and disease severity. Cullen-Frey plots were used to identify age at onset as a log-normal distribution, and χ2 tests were used to test for scale and location mixtures if the onset distribution came from a unique population or was a mixture of distributions representing distinct subpopulations. Because sex was significantly associated with age at onset, mixture of regression with sex as a covariate was used, allowing identification of subpopulations considering covariates. Parametric bootstrapping was used to sequentially test the number of components in various models, and 2 subpopulations were identified. Estimation of distribution of subpopulations was carried out using the expectation maximization algorithm for the mixture of regressions with sex as a covariate.2
Results
Median age at onset for female patients was earlier than male patients (female, 19 years; interquartile range [IQR], 14-28 years; male, 23 years; IQR, 16-35 years; P < .001) (Table). Self-identified Hispanic patients had earlier disease onset (18.5 years; IQR, 14-24 years) than black patients (20 years; IQR, 14-37 years; P = .03) and white patients (20 years; IQR, 15-35 years; P = .02). Two overlapping peaks comprising a bimodal age at onset distribution were identified (Figure, A). Bootstrapping simulations identified 2 subpopulations of disease onset centered around a mean that differed by sex (Figure, B). Hidradenitis suppurativa begins in the mid-teen years in the common onset group (n = 689 [79.2%]) and mid-40s in the late onset group (n = 181 [20.8%]). Of note, the age at onset in the common onset group was significantly earlier in female patients compared with male patients. The estimated location of distribution of age at onset for the common onset group in female patients (n = 500) was 16.8 years (SD, 11.6-24.4 years) and in male patients (n = 189) was 19.7 years (13.6-28.5 years) (P < .001). The estimated location of distribution of age at onset for the late onset group in female patients (n = 125) was 43.5 years (SD, 34.5-54.9 years) and in male patients (n = 56) was 45.2 years (35.9-57.1 years).
Table. Demographic and Clinical Characteristics of All Patients With Hidradenitis Suppurativa in the Cohort.
| Characteristics | Age, y | Comparison for Analysis | P Value | |
|---|---|---|---|---|
| Median (IQR) | % | |||
| Age at presentation (N = 1203) | 32 (23-45) | |||
| Self-reported age at onset (n = 870) | ||||
| All | 20 (15-30) | 100 | ||
| Male | 23 (16-35) | 28.2 | Female vs male | <.001 |
| Female | 19 (14-28) | 71.8 | ||
| Self-reported age at onset across ethnicity (n = 513) | ||||
| White | 20.0 (15-35) | 29.2 | Hispanic vs white | .02 |
| Black | 20.0 (14-37) | 38.0 | Hispanic vs black | .03 |
| Hispanic | 18.5 (14-24) | 25.0 | ||
| Asian | 20.0 (17-29) | 7.8 | ||
| Self-reported age at onset across Hurley stage (n = 658) | ||||
| Hurley stage I | 19 (14-29) | 32.4 | ||
| Hurley stage II | 19 (15-29) | 36.5 | ||
| Hurley stage III | 22 (15.5-35) | 31.2 | Stage I vs stage III | .02 |
Abbreviation: IQR, interquartile range.
Figure. Age at Onset in Patients With Hidradenitis Suppurativa .
A, Overall distribution of all age at onset values showing the bimodal distribution of age at hidradenitis suppurativa presentation. B, Parametric bootstrapping identified 2 components in the mixture of distributions of age at onset (in log10 scale) using sex as a covariate. The estimated distribution for the common onset group centered around the late teen years (blue dot), and a late onset group around the 40s. Bars represent the location and SD range (calculated in the log10) in the original age at onset scale.
Discussion
We report a bimodal distribution for self-reported age at HS onset, with peak common onset occurring in the late teen years and peak late onset occurring in the mid-40s. These findings may help facilitate accurate and timely diagnosis of HS in a previously unrecognized HS subpopulation.
There are several possible reasons why this distribution differs from previous reports. The latter have defined incidence by HS diagnosis, whereas we establish distribution of self-reported age at onset of disease symptoms.3,4 Therefore, these findings are not confounded by diagnostic delay.5 This distribution may be difficult to detect in small cohort studies. Analytic approaches employed in larger data sets may not be optimized to detect this distribution.3,4 Although utilization of ambulatory resources is low in HS, we studied ambulatory data because self-reported age at onset seems most accurately and completely collected in this setting.6
This study is limited by potential recall bias of self-reported age at onset. Recall bias may play a lesser role in the late onset group, in which the time between onset and study entry was likely shorter. This study was also limited by variable disease duration of individuals, thus impairing our ability to assess for differences in disease severity between subpopulations. Despite these limitations, given the overall paucity of data about HS natural history, these findings are an important starting point for future investigation. Large prospective population-based observational studies of rigorously phenotyped patients are needed to further understand the clinical course of HS and unique disease characteristics, prognostic factors, and treatment considerations for these 2 groups.
References
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