The Microbiome in Hidradenitis Suppurativa Tunnels: A Systematic Review.

Hidradenitis suppurativa (HS) is a chronic inflammatory disease that affects the pilosebaceous units, particularly in large skin folds. The pathophysiology of HS is multifactorial, with evidence suggesting that the microbiome plays a crucial role in perpetuating inflammation. The persistent nature of HS tunnels, coupled with potential dysbiosis in these lesions, may help explain the recurrent episodes of HS, even with systemic treatment. To explore this further, a literature search was conducted on June 20, 2024. A total of eight studies, involving 418 patients, 632 HS lesions, 360 HS tunnels, and 300 controls, were included. The findings from these studies suggested that HS tunnels are characterized by a polymicrobial microbiome, predominantly dominated by anaerobic bacteria such as Porphyromonas, Parvimonas, Fusobacterium, and Prevotella. In contrast, HS tunnels exhibit a notable reduction in saprophytic species like Cutibacterium acnes and Staphylococcus epidermidis, which are commonly found in healthy skin. Disease stage, as classified by the Hurley system, is the most significant factor influencing the microbiome composition of HS tunnels, with advanced lesions showing a greater presence of dysbiotic and pathogenic flora. Interestingly, no significant differences in bacterial colonization were observed based on variables such as sex, age, smoking status, body mass index (BMI), or anatomical location. Larger biofilms with active bacteria were found in tunnels and anaerobic regions of hair follicles. Overall, these results highlight the distinct polymicrobial, predominantly anaerobic bacterial flora of HS tunnels and the significant reduction in commensal bacteria typically found in healthy skin. This specific microbiome may help explain both the pathogenic characteristics and therapeutic challenges associated with HS tunnels.