A 28-year-old woman presents with a 4-year history of recurrent, exquisitely painful nodules and abscesses in the axillae and inframammary folds that have progressed to form interconnected sinus tracts and rope-like scars. She reports significant impairment of quality of life and work capacity. The condition shown at **A** in the diagram is being evaluated for biologic therapy. Which of the following best explains the primary pathogenic mechanism underlying the lesions in this condition?

Explanation

## Why "Follicular occlusion with hyperkeratosis, follicular rupture, and spillage of keratin into the dermis triggering innate immune response with neutrophil and Th17 cell infiltration" is right Hidradenitis suppurativa (acne inversa), shown at **A**, is fundamentally a disease of the FOLLICULAR EPITHELIUM, not the apocrine glands despite its historical name. The currently accepted pathogenic model centers on FOLLICULAR OCCLUSION as the primary initiating event: hyperkeratosis and dilation of the terminal hair follicle leads to follicular rupture, spillage of keratin and follicular contents into the dermis, and a brisk innate immune response characterized by massive infiltration of neutrophils and Th17 cells driven by IL-1, IL-17, IL-23, and TNF-alpha. Secondary bacterial colonization (commensal staphylococci, anaerobes) then amplifies the inflammatory cascade. This mechanism directly explains the recurrent painful nodules, abscess formation, and sinus tract development seen in this patient (Bolognia Dermatology 5e Ch 38). ## Why each distractor is wrong - **Primary inflammation of apocrine glands with secondary bacterial colonization**: This reflects the outdated historical understanding of HS. Modern evidence clearly demonstrates that HS is a disease of the FOLLICULAR EPITHELIUM, not primarily apocrine glands. Although lesions occur in apocrine-rich intertriginous areas, the pathology is follicular, not apocrine. - **Comedone formation on the face and trunk with progression to nodulocystic lesions driven by Propionibacterium acnes**: This describes acne conglobata (option C in the label key), not hidradenitis suppurativa. While both involve follicles, acne conglobata presents with comedones and nodulocystic lesions on the face and trunk, lacks the chronic sinus tract formation and scarring characteristic of HS, and has a different pathogenic driver (P. acnes rather than follicular occlusion with innate immune activation). - **Granulomatous infiltration of the dermis with formation of perianal fissures and skin tags secondary to intestinal inflammation**: This describes cutaneous Crohn disease (option D in the label key), which is a granulomatous manifestation of inflammatory bowel disease. Although Crohn disease is a risk factor for HS, it is a distinct entity with granulomatous pathology and "knife-cut" perianal fissures, not the follicular occlusion and innate immune mechanism of HS. **High-Yield:** HS = follicular occlusion (not apocrine disease) → follicular rupture → innate immune storm (neutrophils + Th17 + IL-17/IL-23/TNF-α) → recurrent abscesses, sinus tracts, scars in intertriginous areas; smoking cessation and TNF-α inhibitors (adalimumab) are cornerstone therapies. [cite: Bolognia Dermatology 5e Ch 38; PIONEER I/II adalimumab trials NEJM 2016]