Dissecting Cellulitis and Hidradenitis Suppurativa: Two Diseases or One Follicular-Occlusion Spectrum?

Dissecting cellulitis of the scalp (DC) and hidradenitis suppurativa (HS) share follicular occlusion, rupture, suppuration, tunnel formation, and scarring, yet are usually classified as separate diseases. Whether DC represents a site-modified scalp phenotype of the same core inflammatory process remains unresolved. To examine the DC-HS boundary and assess whether current evidence favors two distinct diseases or one follicular-occlusion spectrum, we performed a structured PubMed-based critical narrative review through June 25, 2026, evaluating direct comparative evidence and five prespecified domains: clinical morphology, topography, histopathology/pathobiology, follicular-occlusion clustering, and therapeutic response. Direct comparative evidence remains limited. A prospective trichoscopy study identified DC-compatible findings in 8 of 23 men with HS (35%). Across independent domains, however, the convergent pattern is more consistent with a shared core follicular-occlusion pathology whose phenotype may be modified by anatomical site than with two wholly unrelated processes. The current operational definition of scalp HS also creates a diagnostic paradox: an apparently similar scalp phenotype may be labeled scalp HS when intertriginous HS is present, but DC when it is isolated. This supports testing whether extra-scalp HS is a contextual classifier rather than a biological discriminator. We propose DC as a plausible scalp-predominant, site-modified phenotype within the HS/follicular-occlusion spectrum, while emphasizing that molecular equivalence is not yet proven. Resolving this distinction could affect trial eligibility, testing of HS-targeted therapies in DC, reciprocal screening, and outcome-measure development.