¹Department of Dermatology and Skin Science, University of British Columbia, Vancouver, BC, Canada
²Department of Pediatrics, University of British Columbia, Vancouver, BC, Canada
³Division of Dermatology, BC Children’s Hospital, Vancouver, BC, Canada

Conflicts of interest: The authors declare that there are no conflicts of interest.
Funding sources: None.

Abstract:
Hidradenitis suppurativa (HS) is a chronic, recurring inflammatory skin disease that significantly impacts the quality of life of patients.¹ HS is more common in adults and adolescents, although true incidence rates may be underestimated due to a lack of earlier recognition of HS in children.² Pediatric HS is a challenging clinical entity to diagnose and manage. Although considered uncommon, treatment of pediatric HS can drastically improve psychosocial well-being and should be considered in children presenting with recurring painful skin nodules, abscesses, scarring and sinus tracts. Multiple comorbidities are associated with pediatric HS, including depression, anxiety, inflammatory bowel disease, metabolic syndrome, and obesity.³ Medical management of pediatric HS poses a unique challenge given the paucity of literature surrounding efficacy and long-term treatment outcomes in pediatric patients. The purpose of this article is to discuss the epidemiology, pathogenesis, comorbidities, and management of pediatric HS.

Keywords: childhood hidradenitis, early onset hidradenitis suppurativa, hidradenitis suppurativa in children, inflammatory disorders, pediatric dermatology

Introduction

Hidradenitis suppurativa (HS) is a chronic disease involving the follicular unit that typically presents with inflammatory intertriginous lesions.⁴ Depending on severity, cutaneous involvement can manifest as painful nodules, abscesses, sinus tracts, and/or hypertrophic scarring.⁵ HS usually presents in adolescents and adults, and is considered uncommon in children, with an estimated prevalence of less than 2% in prepubescent children.⁶ A recent cross-sectional analysis reported 96.8% of pediatric patients with HS were ≥10 years old, with the highest prevalence reported in patients aged 15-17 years old.⁷ Some have noted that delays in care for pediatric patients may reflect an under-recognition of pediatric HS.⁴ In the adult population, women are more commonly affected by HS in comparison to men. Similarly, pediatric HS is more commonly reported in girls, although the exact prevalence is unknown.⁸ Unfortunately, most literature on pediatric HS is limited to small case series, case studies, or extrapolation from adult studies.⁹ More pediatric focused research is needed to better understand disease burden, prevalence, and treatment.

Pathogenesis

The pathogenesis of HS specific to pediatric patients is not well understood and primarily relies on extrapolation from basic sciences and adults with HS. HS pathophysiology is complex and involves environmental, immunologic, and genetic factors. HS is considered a disorder of follicular occlusion, in which hair follicle dysregulation and inflammation play key roles.¹⁰ As affected hair follicles become occluded and eventually rupture, bacteria and keratin enter the surrounding dermis, promoting an inflammatory state and subsequent lesion formation. Many patients with HS have a positive family history, which has prompted genetic studies.¹¹ Gene mutations that alter antimicrobial peptides and cytokines have been demonstrated in patients with HS.¹² Heterozygous mutations in gamma‐secretase (γ‐S), a protease involved in follicular keratinization regulation have been identified in autosomal dominant forms, supporting a genetic link.^12,13 Gamma-secretase deficiencies have also been associated with impaired sebaceous gland formation and follicle disintegration in mice studies.¹⁴ Some research suggests that patients with early-onset HS appear more likely to have a positive family history.¹⁵ From an immunologic standpoint, both the innate and adaptive immune system play important roles. Decreased expression of antimicrobial peptides may facilitate superficial colonization by bacteria and promote ongoing inflammation through pro-inflammatory cytokines.¹⁶ Pro-inflammatory cytokines involved in HS include but are not limited to interleukin (IL)-1, IL-10, IL-17, IL-22, IL-23, and tumor necrosis factor (TNF)-alpha.^9,16 Other factors that can promote HS pathogenesis and impact disease severity include microbial dysbiosis, microbial colonization, mechanical friction, and hormones.¹⁷ In addition, sinus tracts develop a psoriasiform lining, which tries to recapitulate the epidermis, shedding keratin and causing further inflammation. Hence, persistent lesions still exist despite systemic therapy and deroofing is often curative and essential to include in full-spectrum care.

Clinical Features and Diagnosis

Pediatric HS is a clinical diagnosis based on its typical morphology of deep nodules, cysts, sinus tracts, and fibrotic scars in intertriginous areas. A cross-sectional study assessing the clinical features of children <18 years old (mean age of 15.3 years) with HS reported a similar presenting clinical spectrum to adult-onset disease.¹⁸ Typical sites include those abundant with apocrine glands, such as the axillae, inframammary area, groin, and perianal region. Drainage from involved sites is a commonly reported symptom.¹⁹ There are currently no guidelines regarding investigations for HS in pediatric patients or adults. Laboratory investigations or skin biopsy are unnecessary for diagnosis, but imaging may be considered for operative planning when assessing sinus tracts.¹⁸ Ultimately, given the lack of research and consensus, there are currently no screening guidelines for investigating potential comorbidities in pediatric patients with HS. The Hurley staging system is often used to categorize patients into three disease groups based on their level of severity.²⁰ Stage I includes abscess formation (single or multiple), without sinus tract(s) or scarring, Stage II includes those with recurrent abscesses with sinus tracts and scarring present, and Stage III encompasses diffuse involvement, with multiple abscesses and interconnected sinus tracts.²⁰ The Sartorius scoring system is typically reserved for clinical trials and is not commonly used in clinical practice.8 Another useful scoring system is the International Hidradenitis Suppurativa Severity Score System (IHS4) which is a validated, dynamic assessment of HS severity that encompasses counting nodules, abscesses, and draining sinus tracts/fistulas.²¹ The Hidradenitis Suppurativa Quality Of Life (HiSQOL) scoring system may also be useful for capturing impactful areas of HS such as pain, odor, and drainage, which are not measured by the Dermatology Life Quality Index (DLQI) and should be considered by treatment providers.

Associated Comorbidities

Multiple comorbidities have been associated with pediatric HS, including more hormonal imbalances in comparison to adult populations, with manifestations including acne, premature adrenarche, adrenal hyperplasia, metabolic syndrome, and obesity.⁶ Although the overall association between early-onset HS and premature adrenarche and hormonal imbalance remains unclear, assessing for precocious puberty in children presenting with HS may be an important consideration depending on the clinical presentation. From a database of 870 pediatric patients, an elevated body mass index (BMI) and obesity were higher in comparison to reference population standards, as was the prevalence of smoking.¹⁸ Aside from metabolic syndrome, inflammatory bowel disease (IBD) and spondyloarthropathy have also been shown to be associated with HS.⁹ Patients with Down syndrome have been shown in multiple studies to have an earlier onset of HS although the mechanism behind this remains unknown.⁹ A detailed history, including inquiring about a family history of HS and associated comorbid symptoms and a physical examination should be completed. From a psychosocial perspective, HS can drastically impact quality of life and is associated with significant psychological distress.⁸ Painful, inflammatory lesions can limit children’s ability to play, exercise, or attend school which can contribute to obesity and further worsening of disease.⁶ Furthermore, social stigma surrounding HS can negatively affect psychosocial well-being, especially during the adolescent period. Overall, higher rates of anxiety and depression have been reported in pediatric-aged HS patients compared to those without HS.⁹ A cross-sectional study recently examined the quality of life impacts of HS in 25 pediatric patients aged 12-17 years of age.²² They found that 32% of patients had positive screening results for depression on the Patient Health Questionnaire-2, a depression screening tool.²² The Skindex-Teen questionnaire, an adolescent quality of life questionnaire for skin disease was also used, which demonstrated a higher average score in patients with more moderate-severe HS.²² Overall, clinicians should have a high level of suspicion for psychological comorbidities when treating pediatric patients with HS.

Treatment

Management of HS in the pediatric population is limited given the lack of information surrounding long-term outcomes. Determining the appropriate treatment involves weighing the biopsychosocial impact on the child, disease severity, and side effects of medications or procedures. In general, treatment of HS includes topical or systemic medications and surgical modalities depending on the severity. Lifestyle modifications are typically encouraged for all patients and include smoking cessation, weight management, and avoidance of triggers. Patient and family education should emphasize that HS is a chronic disease without a cure, with treatment focusing on disease and symptom management.

For Hurley Stage I disease, conservative management with topical treatment, such as clindamycin 1% solution, azelaic acid 15%, resorcinol 15%, or combination treatment with clindamycin/ benzoyl peroxide is recommended.⁶ Of note, resorcinol is the only topical treatment with studies completed for HS in adults and is a medication that must be compounded. Topical antiseptics and clindamycin are considered safe for use but may be ineffective for more moderate or severe HS.²³ For non-prescription treatments, laser hair removal has been effective via the Hidradenitis Suppurativa Clinical Response (HiSCR) response in patients with mild-to-moderate disease.²⁴ Supplementation with 100 mg of oral zinc has also been shown to improve HS.²⁵ Concurrent supplementation with 4 mg of copper should be considered to prevent copper deficiency.²⁵ For those where topical treatments fail or children with Hurley Stage II disease, systemic medications can be explored. Systemic antibiotics such as doxycycline, clindamycin with rifampicin, metronidazole, and erythromycin are appropriate for use in children with more severe disease.⁶ Counselling regarding potential tooth discoloration and enamel hypoplasia should be done for patients under 8 years old receiving tetracycline antibiotics.²³ However, antibiotics are not a feasible long-term solution. If there is recurrence after treatment, adalimumab or secukinumab should be considered. Oral finasteride demonstrated improvement in resistant cases from a small pediatric case series, however potential side effects include transient sexual dysfunction in males, and pediatric safety data is lacking, particularly for prepubertal males.²⁶ Systemic retinoids used for the treatment of HS include acitretin and isotretinoin, although these have considerable risks and isotretinoin tends to be more effective in milder, folliculocentric subtypes. The long-lasting teratogenic effects of acitretin make it unsuitable for patients with childbearing potential and isotretinoin in children under 12 years of age has been reported to cause premature epiphyseal closure.²⁷ Importantly, all patients of childbearing potential should be counselled surrounding teratogenic effects where applicable.

In terms of biologics, adalimumab is currently the only approved choice in North America for pediatric patients older than 12 years of age who weigh at least 30 kg.²⁸ Safety data surrounding the use of adalimumab in pediatric patients for HS is limited, although adalimumab has been used effectively in pediatric patients for other inflammatory diseases including Crohn’s disease, psoriasis, and juvenile idiopathic arthritis.²⁹ Secukinumab, an IL-17 inhibitor, is both Health Canada and US FDA approved for treatment of adults with moderate-to-severe HS. Based on clinical studies in adults, it may be a therapeutic option for first- or second-line off-label treatment of pediatric HS patients.^30,31 Overall, dermatologists should have a low threshold to treat systemically and preventatively, as HS is typically a progressive disease that can become less responsive to biologic therapy as time passes and severity increases. Surgical modalities may be another option for older children. Depending on the extent of disease, wide excision and/or minimally invasive deroofing can be considered. A recent cross-sectional study found that surgical excision and deroofing were reported as useful for all 23 pediatric patients assessed, while those treated with simple excision had zero responders in 7 cases treated with simple excision.³² However, a surgical approach is more invasive and carries the risk of infection, scarring, and recurrence.⁹ A retrospective review of 11 patients under 18 years old with a total of 23 operative sites reported an overall complication rate of 87% and a 7% reoperation rate.³³ Remission after a single procedure was reported in 57% of included sites.³³ However, it is crucial to combine both medical preventative treatments with surgical therapy, as success rates are much higher with a combination approach.

Conclusion

Pediatric HS is an understudied and underrecognized disease with significant biopsychosocial impacts. Unfortunately, diagnosis is often delayed given the wide variety of presentations in early disease. Clinicians should consider associated comorbidities such as metabolic syndrome, inflammatory bowel disease, and anxiety and depression. Early recognition, diagnosis, and management are essential in improving quality of life and managing symptoms for children and adolescents with HS. Further research focused on long-term outcomes, associated comorbidities, and medical management is needed to improve our understanding and treatment of pediatric hidradenitis suppurativa.

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