What is hidradenitis suppurativa?
Hidradenitis suppurativa (HS), also called acne inversa, is a chronic inflammatory skin condition that affects apocrine gland-bearing skin in the axillae, groin, and under the breasts. It is characterised by persistent or recurrent boil-like nodules and abscesses that culminate in a purulent discharge, sinuses, and scarring.
HS can have a significant psychological impact, and many patients suffer from anxiety, depression, and impairment of body image.
Hidradenitis suppurativa of the axilla
Who gets hidradenitis suppurativa?
Hidradenitis suppurativa often starts at puberty, is most active between the ages of 20 and 40 years, and in women can resolve at menopause. It is three times more common in females than in males. Associations and risk factors include:
- Family history of HS; 30–40% report at least one other family member affected
- Obesity and insulin resistance (metabolic syndrome)
- Cigarette smoking
- African ethnicity
- Follicular occlusion syndrome: acne conglobata, dissecting cellulitis, pilonidal sinus
- Inflammatory bowel disease, particularly Crohn disease
- Other skin disorders: psoriasis, acne, hirsutism
- Comorbidities: hypertension, diabetes mellitus, dyslipidaemia, thyroid disorders, arthropathies, polycystic ovary syndrome, adverse cardiovascular outcomes
- Drugs: lithium, sirolimus, biologics
- Syndromes
- PAPA syndrome
- PASH syndrome (pyoderma gangrenosum, acne, suppurative hidradenitis)
- PAPASH syndrome (pyogenic arthritis, pyoderma gangrenosum, acne, suppurative hidradenitis).
What causes hidradenitis suppurativa?
Although ‘hidradenitis’ implies an inflammatory disease of the sweat glands, we now know that HS is an autoinflammatory syndrome. The exact pathogenesis is not yet understood. Factors involved in the development of acne inversa include:
- Follicular occlusion
- An abnormal cutaneous or follicular microbiome
- Release of pro-inflammatory cytokines
- Inflammation causing rupture of the follicular wall, destroying sebaceous and apocrine glands and ducts.
What are the clinical features of hidradenitis suppurativa?
Acne inversa can affect single or multiple areas in the axillae, neck, inframammary fold, and inner upper thighs. Anogenital involvement most commonly affects the groin, mons pubis, vulva, scrotum, perineum, buttocks, and perianal folds.
HS is characterised clinically by:
- Open double-headed comedones
- Painful firm papules and nodules
- Pustules, fluctuant pseudocysts, and abscesses
- Draining sinuses linking inflammatory lesions
- Hypertrophic and atrophic scars.
Characteristic lesions of hidradenitis suppurativa
Clinical phenotypes of hidradenitis suppurativa (HS)
| Phenotype | Clinical features |
| Regular HS |
|
| Frictional furuncle |
|
| Scarring folliculitis |
|
| Conglobata |
|
| Syndromic |
|
Clinical phenotypes of hidradenitis suppurativa
How is the severity of hidradenitis suppurativa assessed?
Disease severity and extent is measured by clinical and ultrasound assessment at the time of diagnosis and when monitoring response to treatment. There are a number of severity scales for HS [see guidelines for Hidradenitis suppurativa: severity assessment].
The Hurley system, the most widely used assessment tool, describes three clinical stages.
- Stage I: solitary or multiple isolated abscess formation without sinus tracts or scarring.
- Stage II: Recurrent abscesses, single or multiple widely spaced lesions, with sinus tract formation.
- Stage III: Diffuse involvement of an area with multiple interconnected sinus tracts and abscesses.
Hidradenitis suppurativa in skin of colour
What are the complications of hidradenitis suppurativa?
Complications of HS can include:
- Secondary infection
- Psychological effects and negative impact on quality-of-life
- Pyogenic granuloma
- Lymphoedema: female genital
- Squamous cell carcinoma: male anogenital
- Anaemia of chronic disease.
How is hidradenitis suppurativa diagnosed?
The diagnosis of acne inversa requires all three components of the triad to be met:
- Characteristic lesions
- Typical distribution
- Presence and recurrence of lesions.
Swabs for bacteriology are typically negative, which is a clue to diagnosis. Extensive investigations are rarely required. Investigations may be indicated to exclude a differential diagnosis, for possible complications, to identify comorbidities, or for planned treatment.
What is the differential diagnosis for hidradenitis suppurativa?
Differential diagnoses for hidradenitis suppurativa can include the following conditions.
- Staphylococcal skin infections, including abscesses, carbuncles, and furuncles.
- Cysts, like Bartholin cyst or epidermoid cyst.
- Cutaneous Crohn disease.
- Anogenital Crohn disease.
What is the treatment for hidradenitis suppurativa?
For a detailed evidence-based review of treatment for HS, see Management of hidradenitis suppurativa: an Australasian consensus statement. The following provides important general measures and additional medical treatments.
General measures
General measures for treating patients with hidradenitis suppurativa include:
- Weight loss
- Smoking cessation
- Loose fitting clothing
- Absorbent dressings
- Analgesics
- Management of anxiety and depression; including reassurance that the condition is not infectious or a results of poor hygiene.
Specific medical measures
Specific medical measures for treating hidradenitis suppurativa include:
Topical treatments
- Triclosan/benzoyl peroxide wash
- Topical clindamycin phosphate 1% with benzoyl peroxide
- Topical antibiotics: fusidic acid, dapsone, metronidazole.
Systemic treatments
Antibiotics for bacterial infections
- Short oral course for acute staphylococcal abscess
- Tetracyclines as a single agent
- Prolonged courses of at least three months of combination antibiotics: clindamycin plus rifampicin; tetracyclines plus rifampicin; fluoroquinolone plus metronidazole plus rifampicin
- Intravenous ertapenem.
Other oral treatments
- Hormonal therapies: oestrogens, anti-androgen therapy, leuprolide acetate
- Immunomodulatory treatments: systemic steroids for acute flares, and steroid-sparing agents including ciclosporin, methotrexate, and azathioprine
- Biologics: adalimumab is the only biologic approved in Australia and New Zealand for treating hidradenitis suppurativa [see Tumour necrosis factor inhibitors]
- Others are under investigation in clinical trials
- Adalimumab and other biologics have been reported to paradoxically trigger acne inversa
- Other systemic medical treatments used off-label: metformin, acitretin, dapsone, colchicine, and zinc gluconate.
Surgical and other procedural measures
- Incision and drainage of acute abscesses
- Local excision of persistent nodules, abscesses, and sinuses
- Deroofing and curettage of persistent abscesses and sinuses
- Radical excisional surgery of an entire affected area
- Laser ablation (CO2) of nodules, abscesses, and sinuses
- Laser/light hair removal.
What is the outcome for hidradenitis suppurativa?
Hidradenitis suppurativa tends to improve in pregnancy in those who usually have flares during menstruation. Normal vaginal delivery is possible unless the patient has extensive painful genital lesions.
HS is a chronic scarring condition. Spontaneous remission may occur with time, but scarring persists.
Early diagnosis and treatment are required to minimise lasting damage.