Pediatric Hidradenitis Suppurativa

Introduction

Hidradenitis suppurativa/acne inversa (HS) is a chronic, inflammatory, recurrent, debilitating skin disease of the hair follicle which affects apocrine gland-rich areas of the body. The disease usually presents after puberty, but it can, although uncommonly, also affect adolescents (onset after initiation of puberty, older than 10 to 12 years) and children. Typical clinical symptoms include painful, deep-seated, inflamed lesions (nodules, abscesses), tunnels, and scarring. In this chapter, we present the main aspects of the disease in pediatric populations. The major features of HS in children and adolescents are summarized in Table 29.1 .

Pathogenesis

Pathogenetic mechanisms of HS are not yet fully elucidated. In general, genetic susceptibility, obesity/metabolic syndrome, and smoking have been implicated. A positive family history is often observed in patients with early onset of the disease. Familial occurrence varies from 20% to 55% among different studies, whereas a small Danish cohort of obese children reported a positive family history in 80% (4/5) of the patients. Moreover, genetic predisposition may also lead to pediatric HS. Mutations in the γ-secretase genes complex as well as aberrations in the Notch signaling cascade are implicated in the inflammatory process. Data from case reports or small case series show that early-onset HS is also associated with underlying hormonal disorders, such as precocious puberty, premature adrenarche, or adrenal hyperplasia. These conditions are more commonly seen in children than in adults with HS. In the pathogenetic pathway of pediatric HS, the elevated sensitivity of the pilosebaceous unit to circulating sex hormones has also been postulated. Moreover, apocrine glands may also be secondarily involved. Apocrine glands become active during puberty. They empty their content into the follicular canal and not into the skin surface in contrast to eccrine glands. Keratinocytes of the pilosebaceous unit contain androgen receptors, which may promote follicular plugging due to hyperkeratinization, resulting in inflammation, rupture of follicles, abscess, and tunnel (sinus tract) formation.

Another factor propagating HS in adult and pediatric patients is obesity. Recent data suggest that the majority of patients are overweight or obese, with a reported rate varying from about 50% to 80%. Additionally, obesity is likely associated with a more serious disease course as well as precocious puberty. In a recent multicenter study, patients’ body mass index (BMI) were correlated with the average parent BMI, showing that our therapeutic approach and weight counseling strategies should also include the patient’s family.

Despite being a pivotal player in adult HS cases, smoking habits do not seem to play a key role in cases of early-onset HS. According to recent studies, only a small proportion of pediatric HS patients were active smokers. However, bear in mind that children may be subject to passive tobacco exposure.

Epidemiology

Overall, HS has a prevalence of 0.03% (Europe) to 0.053% (USA) and a calculated prevalence of 0.4%. Pediatric HS seems to represent a rather small cluster of the disease. However, the data regarding disease onset shows a wide age range. Although older reports documented an early onset in 2% of HS patients, a recent study from the Netherlands reported that 8% of patients show a disease onset before the age of 13.5 years, whereas according to an Italian study, 90 out of 235 patients (38%) recalled that the first symptoms occurred before the age of 16. On the other hand, a recent US cohort study presented an overall standardized prevalence of 0.02% for pediatric HS patients (0 to 17) and demonstrated that the pediatric age group only represents 1020 of 47620 documented HS cases in the USA (2.2%), affecting pediatric patients of African American or biracial descent significantly more often. A very young disease onset in prepubertal patients (age 10 years or younger), with or without precocious puberty or premature adrenarche, has only been presented in case reports or small case series.

Clinical Features

HS in pediatric patients is also characterized by the presence of inflammatory nodules, abscesses, tunnels, and scarring in the apocrine gland-rich areas of the body. According to recent data, it seems that most subjects suffer from a mild or moderate disease and show a similar clinical course when compared with adult patients. However, it has been suggested that pediatric patients may not have reached their peak severity. Ethnicity may also affect the clinical course and areas of involvement in HS patients. Cases with excessive scarring and numerous abscesses and sinus tracts have been documented. In most patients, the axillary and inguinal regions are involved, although with varying frequency among different studies. Other affected anatomic areas include the buttocks, the submammary area, and the mons pubis. Additionally, most recent studies have demonstrated a female predominance in cases of early-onset HS.