Trends in Body Mass Index Before and After Diagnosis of Hidradenitis Suppurativa

S. Wright; A. Strunk; A. Garg

Disclosures

The British Journal of Dermatology. 2021;185(1):74-79. 

In This Article

Results

Among the 1610 patients with HS and 29 516 controls who met eligibility criteria, a total of 1284 patients from each group were matched at a 1 : 1 ratio for age, sex, race and baseline year (Table 1). Patients in both groups had a mean age of 39·2 years and were predominantly female (84%) and white (53·2%). African American participants comprised 40·8% of each cohort. Those with HS were more likely to have a smoking diagnosis at baseline compared with controls (17·5% vs. 4·3%).

Average baseline BMI was 31·51 kg m−2 among patients with HS compared with 28·48 kg m−2 among controls. After controlling for age, sex, race and smoking status, average baseline BMI was significantly higher among patients with HS than controls [mean difference 3·03, 95% confidence interval (CI) 2·44–3·62; P < 0·001] (Figure 1). Prior to diagnosis, average increase in BMI per year among patients with HS ( = 0·21 kg m−2, 95% CI 0·19–0·24) was slightly higher than for controls ( = 0·15, 95% CI 0·12–0·17; interaction P < 0·001). There was no statistically significant change in annual BMI among patients with HS following diagnosis ( = 0·07, 95% CI − 0·01–0·15; P = 0·07).

Figure 1.

Average body mass index (BMI) according to time from first hidradenitis suppurativa (HS) diagnosis Average BMI for 1284 patients with HS (solid line) and matched controls (dashed line) plotted against time from HS diagnosis in years, with time 0 corresponding to the date of HS diagnosis. Error bars represent 95% confidence intervals. *For the matched control group, time intervals were 'anchored' around patients' first BMI measurement rather than a diagnosis date.

Average baseline BMI and annual change in BMI stratified by sex are shown in Figure 2a. Among female participants, average baseline BMI was 3·37 units (95% CI 2·73–4·01) higher in patients with HS than controls. Average baseline BMI was 1·27 units (95% CI − 0·20–2·73) higher among male patients with HS than controls. Difference in baseline BMI between patients with HS and controls was significantly larger for women than men (interaction P = 0·01) (Table 2). Prior to diagnosis, average increase in BMI per year among female patients with HS ( = 0·25, 95% CI 0·22–0·27) was slightly higher than for controls ( = 0·17, 95% CI 0·14–0·20). In male patients, average increase in annual BMI was slightly higher among patients with HS ( = 0·04, 95% CI −0·02–0·10) than controls ( = 0·01, 95% CI −0·05–0·07). Difference in rate of BMI increase between patients with HS and controls was similar for men and women (interaction P = 0·27).

Figure 2.

Average body mass index (BMI) according to time from first hidradenitis suppurativa (HS) diagnosis in patients with HS and controls, stratified by sex and age at diagnosis Average BMI for patients with HS and controls, stratified by (a) sex and (b) age at diagnosis plotted against time in years from HS diagnosis, with time 0 corresponding to the date of HS diagnosis. *For the matched control group, time intervals were 'anchored' around patients' first BMI measurement rather than a diagnosis date.

Among patients in each of the race categories, average baseline BMI was higher for patients with HS compared with controls (Table 2). Difference in average baseline BMI between patients with HS and controls was similar for white participants (mean difference 3·32, 95% CI 2·52–4·13), African American participants (mean difference 2·50, 95% CI 1·58–3·42) and patients of other race (mean difference 4·10, 95% CI 1·69–6·50). Similarly, average annual increase in BMI prior to HS diagnosis was somewhat higher for patients with HS compared with controls across all race categories (Table 3). Magnitude of the difference in the rate of BMI change between patients with HS and controls was similar across race categories (interaction P = 0·13).

With respect to age, mean difference in baseline BMI between patients with HS and controls was 4·10 kg m−2 (95% CI 3·15–5·06) for those diagnosed before age 40 years and was 2·38 kg m−2 (95% CI 1·63–3·12) for those diagnosed after age 40 years (interaction P = 0·001) (Figure 2b). BMI increased at a slightly faster rate among patients with HS diagnosed before age 40 years ( = 0·45 per year, 95% CI 0·41–0·49) compared with controls ( = 0·35, 95% CI 0·31–0·39), and also among patients with HS diagnosed after age 40 years ( = 0·07, 95% CI 0·04–0·10) compared with controls ( = 0·02, 95% CI −0·01–0·05). Difference in the rate of BMI increase between patients with HS and controls was similar regardless of age at diagnosis (interaction P = 0·13).

Among tobacco smokers, average baseline BMI was 3·02 units (95% CI 0·07–5·31) higher in patients with HS than controls. Among nonsmokers, average baseline BMI was 3·03 units (95% CI 2·41–3·66) higher in patients with HS than controls. Difference in baseline BMI between patients with HS and controls did not vary significantly according to smoking status (P = 0·99). Among smokers, average annual change in BMI prior to diagnosis was an increase of 0·18 units (95% CI 0·12–0·23) in patients with HS and an increase of 0·17 units (95% CI 0·06–0·29) in controls. Among nonsmokers, average annual change in BMI prior to diagnosis was an increase of 0·22 units (95% CI 0·20–0·25) in patients with HS and an increase of 0·14 units (95% CI 0·12–0·17) in controls. Difference in rate of BMI change for patients with HS vs. controls did not vary significantly between smokers and nonsmokers (interaction P = 0·26). Our primary and subgroup findings remained unchanged in sensitivity analysis using a time-invariant variable to classify 'ever' or 'never' smokers (Tables S1, S2; see Supporting Information).

In exploratory analysis, average annual change in BMI after diagnosis was an increase of 0·27 units (95% CI 0·15–0·40) in patients with HS diagnosed before age 40 years, and an increase of 0·27 units (95% CI 0·15–0·40) in matched controls (Figure 2b, Table S3; see Supporting Information). Average annual change in BMI after diagnosis was −0·05 units (95% CI −0·15–0·05) in patients with HS diagnosed after age 40 years, and an increase of 0·05 units (95% CI −0·05–0·15) in matched controls. Difference in the rate of BMI change between patients with HS and controls after diagnosis was 0·00 units per year (95% CI −0·18–0·18) for those diagnosed before age 40 years, and −0·10 units per year (95% CI −0·24–0·04) for those diagnosed after age 40 years.

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