Previously, a new dichotomous outcome was developed, calculated as 55% reduction in the International Hidradenitis Suppurativa 4 score (IHS4-55). It was validated in datasets of adalimumab and placebo treated HS patients. External validation is an important aspect of clinical outcomes.
We aimed to externally validate the novel dichotomous IHS4-55 in a non-biologic treated dataset of HS patients.
Data from a previously published European-wide prospective clinical study of antibiotic treatment of HS patients was used to assess the association of IHS4-55 achievement with individual reduction in inflammatory nodules, abscesses and draining tunnels. Moreover, the associations between IHS4-55 positivity and achievement of the minimal clinically important differences (MCID) for Dermatology Life Quality Index (DLQI), numerical rating scale (NRS) Pain, and NRS Pruritus were analyzed.
Data was obtained from 283 individual patients, of which 36.4% (103/283) were treated with clindamycin and rifampicin and 63.6% (180/283) with tetracyclines for 12 weeks. Achievers of the IHS4-55 demonstrated a significant reduction the counts of inflammatory nodules, abscesses, and draining tunnels (all p<0.001). Additionally, IHS4-55 achievers had an odds ratio (OR) for achieving the minimal clinically important difference (MCID) of DLQI, NRS Pain and NRS Pruritus of 2.16 (95% CI 1.28-3.65, p<0.01), 1.79 (95% CI 1.10-2.91, p<0.05), and 1.95 (95% CI 1.18-3.22, p<0.01), respectively.
This study shows the external validity of the novel IHS4-55 by demonstrating a significant association between IHS4-55 achievement and a reduction in inflammatory lesion counts as well as achievement of MCIDs for DLQI, NRS Pain and NRS Pruritus in an antibiotic-treated cohort. These findings support the use of the IHS4-55 as a novel primary outcome measure in clinical trials.

The Author(s). Published by S. Karger AG, Basel.