Hidradenitis suppurativa (HS) is a painful, debilitating skin disease that requires the combination of three clinical features to confirm its diagnosis. First, typical deep inflammatory nodules, abscesses, tunnels, and fibrotic scarring must be present. These lesions should evolve chronically or recur and must be located in typical sites such as the axillae, groin, buttocks, and inter- and inframammary folds. HS may also involve the face, scalp, neck, postauricular area, back, and inner thighs.1 HS is associated with decreased quality of life because it can lead to major disfigurement. Therefore, early recognition is essential to prevent late complications. Unfortunately, a definitive diagnosis of HS may take several years because the lesions can resemble other conditions.2

The prevalence of HS ranges from less than 1% to 4% of the global general population.3 It has been suggested that HS and acne vulgaris (AV) can coexist.4 However, no study has specifically focused on the prevalence of HS among patients with acne. After encountering multiple cases of HS in the acne population, with some cases remaining unrecognized for years, we conducted a study to assess the rate of HS in a sample of Lebanese patients with acne.

A cross-sectional study was conducted from May to December 2022. Data were collected in Lebanon by 5 dermatologists who examined each acne patient for additional signs of HS. HS severity was assessed using the Hurley staging system, which includes 3 stages. Stage I consists of single or multiple abscesses without sinus tracts or scarring. Stage II includes recurrent abscesses with sinus tracts and scarring. Stage III is characterized by diffuse involvement with multiple interconnected sinus tracts and abscesses across the entire affected area, along with scar formation.5

The total sample comprised 310 participants with a mean age of 22.63±6.90 years; 78.7% were female. The mean age of acne onset was 17.56±5.91 years, whereas the mean age of HS onset was 20.25±7.09 years. Overall, 21.6% (n=67) also had HS, and 1.3% (n=4) had previously been misdiagnosed with acne instead of HS (Tables 1 and 2).

Our study showed that the prevalence of HS in the acne population was 21.6%. Most patients with HS presented lesions in the axillae and groin. The most common severity stages, in descending order, were Hurley II, Hurley I, and Hurley III. These findings support a possible similarity in the pathophysiology of HS and AV. Both conditions originate from folliculopilosebaceous units and share a similar inflammatory mechanism involving the innate immune system, with particular emphasis on interleukin-1 as a key cytokine.6,7 Furthermore, both conditions may coexist as part of the follicular occlusion tetrad, which includes acne conglobata, hidradenitis suppurativa, pilonidal sinus, and dissecting cellulitis of the scalp.8

Despite these similarities, important differences exist between these conditions. Acne pathophysiology involves follicular hyperkeratinization, hyperseborrhea, and dysbiosis of the skin microbiome induced by Cutibacterium acnes.9 In contrast, HS involves follicular occlusion followed by dilatation and rupture,2 typically accompanied by a sterile inflammatory response.10

To our knowledge, this is the first study to investigate the prevalence of HS among patients with acne. Conversely, the prevalence of AV among patients with HS has previously been studied, showing a prevalence of 15.2% among patients with HS compared with 2.9% among individuals without HS.4

Additionally, the global prevalence of HS in the general population varies widely, ranging from less than 1% to 4%.3 However, HS prevalence may be underestimated due to frequent misdiagnosis.2 In our study, misdiagnosis of HS as acne was observed in 4 patients (1.3%). Indeed, there is some overlap in the topographic distribution of these two conditions. Certain typical acne sites – such as the face, chest, and back – may also occasionally be affected by HS. Although HS typically produces deeper lesions with distinctive clinical features, previous research has shown that HS may occasionally be clinically indistinguishable from severe AV lesions.2

Underdiagnosis and misdiagnosis of HS remain persistent challenges. Given that our study identified a high rate of HS (21.6%) among patients with acne and considering the substantial negative impact HS has on quality of life,2 clinicians should maintain a high index of suspicion for HS in patients presenting with acne.

This study has several limitations. First, due to the cross-sectional design, the results represent a single point in time and causality cannot be established. Second, selection bias may exist because the sample was conveniently recruited from specific dermatology clinics.