Hidradenitis suppurativa (HS) is a chronic inflammatory skin disorder characterized by recurrent nodules, abscesses, comedones, and sinus tracts that often leave prominent scarring in the axilla, groin, perianal, inframammary, and intermammary folds [1,2,3]. HS is more prevalent in women than men and affects up to 4% of the global population, with an estimated annual cost of $6500 per patient [4]. In one study, nearly half of the patients indicated that they could not afford the dressings and wound care supplies they would prefer in terms of both type and quantity [4].

Additionally, HS negatively impacts quality of life, as the lesions can be painful, disfiguring, and malodorous, hindering activities of daily living [5,6,7]. Specifically, one study demonstrated that said features of HS can result in significant impairments that commonly exceed other dermatoses, including psoriasis, atopic dermatitis, and acne vulgaris. Due to the severity of HS, significant psychological distress and psychiatric comorbidity may be concomitantly observed with the disease. Patients with HS endure a compromised quality of life, battling excruciating pain, recurrent abscesses, and chronic inflammation. The condition’s physical and emotional toll often leads to limited mobility, social isolation, and a profound impact on their overall well-being [8]. Unfortunately, treatment courses are often partially efficacious, and many patients are left with the aforementioned sequalae [8].

Although the exact pathophysiology of HS is unclear, the prevailing theory is that the condition is caused by the follicular occlusion of the folliculopilosebaceous unit, followed by rupture and inflammation [9,10,11]. Furthermore, a mutation in the γ-secretase enzyme that leads to the failure of keratin degradation has been linked to HS [12,13]. Risk factors include obesity, hormonal changes experienced during the postpartum and premenopausal states, stress, family history, and environmental factors such as smoking and mechanical friction [14]. Shaving or waxing, as well as friction from tight clothing, can aggravate inflammation by further disrupting hair follicles [14,15].

HS is a chronic condition characterized by inflammation, pain, pus formation, tissue damage, and scarring. Immune cells and cytokines play a significant role in the development of HS [16]. Keratin fibers and other debris from tissue destruction and scarring activate Toll-like receptors (TLRs) on macrophages and dendritic cells, leading to the production of the pro-inflammatory cytokines, tumor necrosis factor alpha (TNF-α), interleukin (IL)-17, and IL-1β [17]. The NLRP3 (nucleotide-binding domain, leucine-rich family pyrin domain containing 3) inflammasome is the best-characterized inflammasome and is activated by the release of material from follicles, leading to the production of IL-1β and neutrophil involvement [18]. HS lesions have reduced levels of IL-22, leading to an increased production of IL-10 due to increased IL-1β [1,19,20]. This intricate interplay between immune cells and cytokines creates a self-sustaining cycle of inflammation, causing recurrent pain, purulence, tissue damage, and scarring in HS patients [21].

These findings emphasize that comprehensive management is crucial in treating HS, with various treatments available depending on the severity of the condition [22]. Mild cases are treated with topical clindamycin and dapsone, while stages 1 and 2 HS involve combining rifampin with either oral clindamycin or minocycline. These antibiotics function to reduce inflammation, infections, and new lesions in HS. Prolonged antibiotic regimens are often used to control HS; however, this strategy may be inducing antibiotic resistance. One study found that lesions of HS patients on prolonged antibiotics grew significantly more antibiotic-resistant bacteria. These results underscore the importance of antibiotic stewardship when managing HS [23]. Alternatively, hormonal treatments such as oral contraceptives, spironolactone, and finasteride have also been used as adjuncts in severe disease or in mild-to-moderate presentations. As increased levels of androgens cause the folliculopilosebaceous gland to secrete more sebum, the mechanism of hormone therapy to treat HS functions by balancing testosterone and 5-dihydrotestosterone (5-DHT) levels [23]. Severe cases may require treatments like adalimumab, intravenous carbapenems, isotretinoin, laser therapy, and surgical excision. Adalimumab is a monoclonal antibody that targets TNF-alpha, blocking the inflammation that contributes to abscess, inflammatory nodules, and draining tunnels. Carbapenems function as broad-spectrum antibiotics, and isotretinoin inhibits keratinization and sebaceous gland function, resulting in smaller glands that are less likely to be clogged. Surgical interventions for HS encompass procedural approaches like laser therapy and minor surgical procedures, including incision and drainage or deroofing. A more extensive surgical option for severe disease would be wide local excision [23]. Laser Speckle Contrast Analysis (LASCA) is an innovative tool with diverse applications in dermatology and dermatosurgery. It measures speckle contrast to assess local blurriness in images, linked to tissue blood perfusion. LASCA effectively estimates skin microcirculation and aids in HS evaluation. It detects imperceptible foci and post-operative outcomes, including ischemic necrosis and lesion area assessment for surgical precision [4,23].

The diagnosis of HS is primarily a clinical one; however, histopathology is the gold standard for a definitive diagnosis [22]. Clinical diagnosis is made by the modified Dessau definition, which assesses the type of lesions, their location, and the patient’s medical history [23,24]. Specifically, three diagnostic criteria must be present [25]. First, there must be the presence of deep-seated painful nodules or other characteristic lesions, which can resemble abscesses, bridged scars, draining sinus, or post-inflammatory, open, tombstone double-ended comedones. Second, the lesions must appear in one or more of the predilection areas, including the axillae, inframammary and intermammary folds, groin, perineal region, or buttocks. Lastly, the disease must be chronic and recurrent, with at least two recurrences over a six-month period [25].

Other factors, including a family history of HS, recurrent uncharacteristic lesions, and the absence of pathogenic microbes, may also support the diagnosis [26]. The clinical presentation of painful lesions in the predilection areas, along with their recurrent and chronic nature, is usually sufficient for a self-reported diagnosis with a high degree of accuracy [27]. However, an observation period may be necessary to confirm the diagnosis in cases where there is no history of recurrence and chronicity, with a delay in diagnosis not exceeding six months [28].

As such, a more objective method for the diagnosis of HS is necessary. In recent years, non-invasive imaging techniques have grown in popularity for the assessment of the extent, inflammatory activity, vascularization, and treatment response of HS lesions. Imaging methods can also help prevent misdiagnosis and reduce diagnostic delays when HS is suspected [29]. However, there are limited publications on the subject.

Fluorodeoxyglucose positron emission tomography (FDG-PET) measures the metabolic activity of the cells in body tissues, allowing for the detection of inflammation, cancer, and infection [30,31]. While FDG-PET imaging is primarily used in the field of oncology, it has proven useful in other medical areas of cardiac and brain imaging. FDG-PET is known for its high sensitivity in detecting cellular inflammation in tissues and early signs of atherosclerosis [32]. Specifically in dermatology, FDG-PET has been used to ascertain systemic and vascular inflammation in psoriasis, detecting inflammatory lesions in the skin, blood vessels, joints, and liver [33]. Tissues that are hypermetabolic and inflamed exhibit a greater uptake of FDG compared to surrounding tissues, due to increased glucose uptake and vascularity. This distribution of FDG throughout the body allows clinicians to identify hypermetabolic tissues, as well as inflammatory and infectious conditions [29].

2. The Role of FDG-PET in the Evaluation of Hidradenitis Suppurativa