Hidradenitis suppurativa (HS), a chronic inflammatory disease of the apocrine gland-bearing skin, leaves dermatologists without a validated tool to distinguish a true inflammatory flare from progressive loss of biologic response. The diagnostic gap carries direct consequences for treatment switching.

Why the distinction carries weight

HS affects an estimated 0.1% to 1% of adults in Western populations, with higher documented prevalence in women and patients of African descent. Painful lesions cluster in the axillae, groin, and inframammary folds, where Hurley stages I through III classify severity by abscess count and tunnel burden. Misreading a flare as failure may push a patient toward an unnecessary biologic switch, while mistaking failure for a flare may delay effective escalation by months. The caveat: switching costs and escalation delays are rarely measured in HS trials, so the real-world penalty for either error remains unquantified.

What tools clinicians actually have

Clinicians typically lean on lesion counts, the patient-reported visual analog scale for pain, and the International Hidradenitis Suppurativa Severity Scoring System (IHS4, a composite score of nodules, abscesses, and draining tunnels). No serum or imaging biomarker reliably discriminates flare from loss of response. Ultrasound can reveal subclinical tunnels that explain a recurring lesion, but it does not label them as flare versus failure, a limitation ultrasound vendors do not emphasize in promotional material.

Why the field has not closed the gap

The reason this distinction matters more now than five years ago is the crowded late-stage pipeline. Adalimumab remains the only biologic with United States regulatory approval for moderate-to-severe HS, while secukinumab and bimekizumab have accumulated phase 3 evidence in the indication. With multiple mechanisms of action competing for the same patients, the threshold for declaring a biologic failed carries pharmacoeconomic weight that an individual prescriber cannot fully absorb.

What the existing endpoints cannot capture

Trials of HS biologics report week-12 or week-16 response rates, with non-responders defined by absolute IHS4 reduction rather than by clinical judgment about flare pattern. That endpoint is well-suited to regulatory comparison but poorly suited to the bedside question. A patient with a new abscess every eight weeks looks the same in week 16 as a patient with progressive tunnel extension; the binary metric does not separate them.

What the Dermatology Times framing leaves unsaid

What remains absent from the discussion is a standardized flare definition. Patient-reported flare frequency, intercurrent antibiotic exposure, and the trajectory of subclinical ultrasound findings are not captured by current endpoints. A flare should, in principle, resolve with continuation of an effective therapy, while true loss of response should not; yet flares can last weeks, biologics drift in efficacy over months, and missed doses confound every longitudinal count.

A standardized flare definition would let trials measure durability rather than snapshots. Until investigators, regulators, or payers absorb the methodological cost of validating such a tool, dermatologists will continue to make switching decisions on a clinical impression that the literature does not formally support.