Hidradenitis suppurativa

What is hidradenitis suppurativa?

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disorder that affects apocrine gland-bearing skin, typically the axillae, groin, perianal region, buttocks, and inframammary folds. It is characterised by persistent, deep-seated, painful nodules and abscesses that can progress to sinus tract formation, purulent discharge, and scarring.

Also known as acne inversa, this disorder can significantly impact quality of life and is associated with several disease-modifying comorbidities, including metabolic syndrome and psychiatric disorders.

Mild axillary HS showing scars and post-inflammatory erythema 

Marked comedones in axillary HS 

Nodules and sinus formation in axillary HS 

HS in the groins spreading down to the upper thighs 

An acute painful inflammatory nodule in axillary HS 

Severe axillary HS with scars and sinus formation 

Submammary HS 

Inflammatory HS in the groin with multiple painful nodules 

Who gets hidradenitis suppurativa?

The global prevalence of hidradenitis suppurativa is estimated to range from 0.1% to 4%. However, underdiagnosis and misdiagnosis likely mean that the actual prevalence is higher. Delayed diagnosis is also common.

HS typically presents following puberty by the second to third decades of life. Studies show that there is no racial predilection, although some surveys suggest it may be more common in African Americans.

Risk factors for the development of HS:

• Sex — Female-to-male ratio of approximately 3:1 in Western countries, though perianal disease tends to be more common in men.
• Family history — One-third of patients report an affected first-degree relative.
• Obesity — Likely related to increased skin fold friction and chronic systemic inflammation; childhood obesity is correlated with a higher risk of early-onset HS.
• Cigarette smoking — Possibly related to delayed wound healing and follicular occlusion due to nicotine and other components.
• Mechanical stress.

Associated comorbidities:

• Metabolic syndrome
• Type 2 diabetes mellitus
• Cardiovascular disease
• Polycystic ovary syndrome (PCOS)
• Acne
• Depression, anxiety, and suicidal ideation
• Other immune-mediated diseases eg, inflammatory bowel disease, spondyloarthropathy, non-infectious uveitis (possible association)
• Abdominal aortic aneurysm (slightly increased incidence).

What causes hidradenitis suppurativa?

The exact cause of hidradenitis suppurativa is not fully understood. HS is described as an autoinflammatory syndrome, and its development is influenced by genetic, immune, hormonal, microbial, mechanical, and lifestyle factors. Hidradenitis suppurativa is not contagious, and it is not caused by poor hygiene.

The early pathogenesis of HS is thought to involve follicular occlusion and rupture, an abnormal innate immune response, and a subsequent inflammatory cascade.

Leukocytic infiltration, oedema, and bacterial dysbiosis within ruptured follicular units lead to inflammatory nodules and abscesses.

Persistent inflammation results in extensive fibrosis, and late signs of HS consist of epithelial-lined, pus-draining tunnels deep in the dermis.

What are the clinical features of hidradenitis suppurativa?

Hidradenitis suppurativa is characterised by:

• Open and closed comedones
• Painful firm papules and nodules
• Pustules and fluctuant pseudocysts
• Abscesses
• Draining sinuses
• Hypertrophic or atrophic scarring with deformity

Hidradenitis suppurativa typically affects intertriginous areas and can affect one or multiple sites:

• Axillae
• Neck
• Breasts
• Inframammary folds
• Sub-abdominal folds
• Inner upper thighs
• Groin
• Mons pubis
• Vulva/scrotum
• Perineum
• Buttocks
• Perianal area.

Clinical phenotypes

Follicular

• This subtype tends to have an earlier age of onset and is characterised by nodules and comedones.
• There is a greater incidence of concomitant papular and nodular acne.
• The disease trajectory is less aggressive, with abscesses seen infrequently.

Inflammatory

• This subtype is particularly aggressive and has a greater incidence of abscesses and fistular tracts, which can coalesce into scarring plaques.
• Odour and pain are experienced more frequently.

Mixed

• Folliculitis and/or comedones are common, interspersed with abscesses.
• Individuals are predisposed to develop epidermal cysts, and postinflammatory hyperpigmentation may occur.
• Tunnels are not rare, but are often thin and non-branching.
• Progression is usually mild.

Syndromic

Hidradenitis suppurativa can also occur within rare autoinflammatory syndromes:

• Follicular occlusion syndrome: acne conglobata, dissecting cellulitis, pilonidal cyst
• PASH syndrome: pyoderma gangrenosum, acne, suppurative hidradenitis
• PAPASH syndrome: pyogenic arthritis, pyoderma gangrenosum, acne, suppurative hidradenitis
• PsAPASH syndrome: psoriatic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa
• PASS syndrome: pyoderma gangrenosum, acne, hidradenitis suppurativa, ankylosing spondylitis
• SAPHO syndrome: synovitis, acne, pustulosis, hyperostosis, osteitis.

How is the severity of hidradenitis suppurativa assessed?

There are several severity scales to assess hidradenitis suppurativa clinically and academically.

Hurley Staging

This is the most commonly recognised clinical scoring system:

• Stage I — Single or multiple abscesses without sinus tracts and scarring
• Stage II — Recurrent abscesses with sinus tracts and scarring
• Stage III — Diffuse or multiple interconnected sinus tracts and abscesses across the entire area

The Hurley staging system is not a dynamic means of assessment. Once a stage is reached, it cannot be downgraded due to the irreversibility of scarring with medical therapy.

International Hidradenitis Suppurativa Severity Score (IHS4)

IHS4 is a dynamic scoring tool that can be particularly helpful in monitoring disease progression and response to treatment.

Mild: <3 points
Moderate: 4-10 points
Severe: >11 points

Revuz-Modified Sartorius Score

This score is made by counting involved regions, nodules, and sinus tracts. Its use has declined due to its complexity and the introduction of other measures such as the IHS4.

The Hidradenitis Suppurativa Quality of Life (HiSQOL) score

The HiSQOL is used to consider the degree of pain, the number of flares, and the impact on daily life in hidradenitis suppurativa. This is a reliable and valid tool to measure HS-specific health-related quality of life.

The Hidradenitis Suppurativa Clinical Response (HiSCR)

HiSCR is defined as a reduction in inflammatory lesion count (ie, abscesses, inflammatory nodules) and no increase in abscesses or draining fistulas, when compared with baseline.

It is predominantly used in clinical trials as a dichotomous outcome to assess the effectiveness of treatment with biologics. It has limited use in clinical practice.

The most commonly used scores are: HiSCR50, HiSCR75, and HiSCR90, representing a 50%, 75%, and 90% reduction in inflammatory lesion counts as compared to baseline, respectively.

What are the complications of hidradenitis suppurativa?

• Permanent scarring
• Secondary infection
• Psychosocial morbidity and reduced quality of life
• Chronic pain and impaired mobility
• Lymphatic obstruction and lymphoedema
• Squamous cell carcinoma
• Anaemia of chronic disease
• Systemic amyloidosis

How is hidradenitis suppurativa diagnosed?

Hidradenitis suppurativa is primarily diagnosed clinically, based on the modified Dessau criteria.
Diagnosis requires fulfilment of all three components:

1. Typical lesions (nodules, abscesses, sinus tracts, and/or fibrotic scars)
2. Typical distribution (intertriginous areas)
3. Recurrence and chronicity of lesions (≥2 episodes over 6 months)

Diagnosis is supported by:

• Positive family history of hidradenitis suppurativa
• Negative microbiology swab of affected skin.

Biopsy is not typically needed, but it can help exclude other conditions eg, if there are features suggestive of squamous cell carcinoma. Histological features of HS include:

• Follicular occlusion
• Follicular hyperkeratosis
• Follicular epithelial hyperplasia
• Epidermal psoriasiform hyperplasia
• Perifollicular inflammation.

Imaging is not necessary for diagnosis. However, ultrasound can help identify subclinical features, and MRI is useful for assessing complications and the extent of anogenital disease.

What is the differential diagnosis for hidradenitis suppurativa?

• Staphylococcal skin infections, including abscesses, carbuncles, and furuncles
• Cysts eg, Bartholin cyst, epidermoid cyst
• Cutaneous Crohn disease
• Anogenital Crohn disease

What is the treatment for hidradenitis suppurativa?

Optimal management of hidradenitis suppurativa requires a multidisciplinary team approach consisting of dermatology, general and/or plastic surgery, general practice, wound care management, dietetics, weight management services, and psychology.

Treatment should be tailored to each individual and follow local or regional management guidelines, where available.

General measures

• Patient education with reassurance that the condition is not infectious nor a result of poor hygiene
• Assess quality of life impact with HiSQOL, along with lesion count and frequency of flares
• Record the Hurley Stage and consider immediate referral to secondary care dermatology for stage II-III disease
• Screen for and manage comorbidities eg, metabolic syndrome, cardiovascular disease, depression/anxiety, PCOS, diabetes mellitus, etc
• Smoking cessation
• Weight management — consider a GLP-1 agonist if obese, especially in the presence of associated comorbidities
• Wound care — absorbent dressings with atraumatic adhesives are recommended
• Pain management eg, oral paracetamol and NSAIDs (first-line), opioids (cautious use), anticonvulsants or antidepressants (for neuropathic pain)
• Pruritus management eg, topical corticosteroids, oral first-generation antihistamines

Specific measures

Outlined below are commonly utilised treatments for hidradenitis suppurativa.

Medical therapy

Topical treatments

May be used alone for mild HS or as adjunctive therapies in more severe disease:

• Topical clindamycin 1% lotion/gel/cream
  • Applied twice daily to affected regions
• Ruxolitinib 1.5% cream
• Topical antiseptics eg, 4% chlorhexidine gluconate solution
  • Limited evidence base but frequently used according to patient preference
• Magnesium sulphate paste
  • Draws pus from boils and carbuncles for acute relief

Intralesional treatments

Triamcinolone acetonide 10–40 mg/mL injections to individual inflammatory lesions; may require repeat sessions on a weekly to three-monthly basis.

Systemic treatments — Antibiotics

• Short-course antibiotics are used for superimposed bacterial infections.
• Longer courses of antibiotics are used in HS for their presumed immunomodulatory properties.
• Always follow local antibiotic guidelines.

Systemic treatments — Biologics

Biologics should be initiated in the case of inadequate disease control from the above treatments. Three biologics have been licensed for the treatment of HS: adalimumab, secukinumab, and bimekizumab.

There is also limited data to support the use of infliximab, ustekinumab, and brodalumab in moderate to severe HS.

Other systemic agents

• Systemic corticosteroids
  • May be helpful as short-term rescue medication for acute flares
  • High dose used eg, 0.5–0.7 mg/kg/day oral prednisolone equivalent
  • Rapid tapering is required
• Acitretin
  • 0.25-0.50 mg/kg/day
  • Use only in males or non-fertile females if scarring folliculitis is present
• Dapsone
  • Up to 200mg/day for a minimum of 3 months may be considered
• Metformin modified release
  • Start from 500 mg once daily and, if tolerated, titrate up to 2-3 g daily over weeks
• Colchicine
  • 0.5-2.5 mg/day
• Anti-androgen therapy
  • Oral contraceptives
  • Spironolactone (25-100 mg/day)
  • Only for use in non-pregnant women, especially those with features of hyperandrogenism or PCOS
• Zinc gluconate
  • 90 mg/day in mild-moderate HS

Future treatment options

Therapeutics in phase II/III development include:

• Amlitelimab (OX40 inhibitor)
• Eltrekibart (CXCR 1/2 inhibitor)
• Lutikizumab (IL-1α/β inhibitor)
• Povorcitinib (JAK1 inhibitor)
• Remibrutinib (BTKi inhibitor)
• Sonelokimab (IL-17A/F nanobody)
• Spesolimab (IL-36 inhibitor)
• Upadacitinib (JAK1 inhibitor)

Surgery

Surgery is an effective treatment that should be used in combination with lifestyle and medical intervention. Small nodules are ideally addressed early to prevent rupture of blocked follicles and the subsequent development of chronic, interconnecting sinus tracts.

It is usually safe to continue biological treatments whilst undergoing surgery, but specialist surgical opinion should be sought on an individual basis.

Procedural options are listed below:

Incision and drainage

• Lesion type: acute abscesses
• For immediate relief, but has an almost 100% chance of recurrence
• Wound closure with secondary intention healing

Deroofing (unroofing)

• Lesion type: persistent nodules, abscesses, and sinus tracts
• Wound closure with secondary intention healing

Wide local excision

• Lesion type: persistent nodules, abscesses, and sinus tracts
• Wound closure with primary closure or secondary intention healing

Radical excisional surgery

• Removes the entire affected area
• Wound closure with skin flap repair, secondary intention healing, or negative pressure wound therapy

Risks of surgery include wound breakdown, numbness, several months of post-operative healing, and lesion recurrence.

Non-standard physical therapies

Hair removal may be considered in non-inflammatory HS using laser therapy (eg, Ng:Yag, alexandrite, or diode lasers) or intense pulsed light therapy.

This may improve pain and slow disease progression by destroying the folliculo-sebaceous unit, thereby reducing follicular blockage and decreasing bacterial presence.

What is the outcome for hidradenitis suppurativa?

Hidradenitis suppurativa is a genetically driven, chronic scarring condition that can significantly impair quality of life if left untreated. Spontaneous remission or reduced inflammation may occur over time (eg, after menopause in women), although scarring persists. Early diagnosis and treatment are essential to minimise lasting damage.