Hidradenitis Suppurativa

Overview

Definition

Hidradenitis suppurativa (HS), also referred to as acne inversa, is a chronic inflammatory skin condition due to occlusion of apocrine sweat glands and hair follicles.

Epidemiology

• Prevalence of HS is approximately 1%–4% globally.
• 3 times more common in women than men
• Usual age of onset is 12–40 years.
• Rarely seen in children before puberty
• More common in the African American population

Etiology

Hidradenitis suppurativa develops due to blockage of hair follicles and the ducts of sweat glands in the skin. Risk factors include:

• Smoking
• Obesity
• Genetic susceptibility: Approximately 40% of patients have a positive family history.
• Mechanical stress (friction caused by wearing tight clothes)
• Hormonal changes: ↑ severity during the perimenstrual period in women
• Medications:
  • Medroxyprogesterone acetate
  • Levonorgestrel intrauterine device
  • Lithium

Pathophysiology

Normal physiology

The skin is mainly composed of 3 layers:

• Epidermis (outer layer):
  • Serves as a barrier, protects from infections
  • Helps in tactile sensation
• Dermis (middle layer): contains blood vessels, nerves, hair follicles, and sebaceous and sweat glands
• Hypodermis (inner layer): contains fat and connective tissue

Pathophysiology of HS

The exact pathogenesis of HS remains unclear; the initial event in the development of HS is follicular occlusion.

• Apocrine exocrine glands secrete sweat into hair follicles in the dermis.
• Ductal keratinocytes proliferate, incited by:
  • Excessive hormonal stimulation 
  • Nicotine/smoke
• Accumulated keratin debris → immune reaction → folliculitis and follicular blockage
• Keratinocytes cause mechanical plugging. 
• Pilosebaceous structures rupture → 
  • Release of keratin fragments, hair, and sebum
  • Inflammatory cells accumulate.
• Repeated acute reactions result in chronic granulomatous inflammation and suppuration secondary to bacterial proliferation.

Clinical Presentation

The primary sites of involvement for HS are the intertriginous skin areas of the axillary, groin, perianal, perineal, and inframammary regions, though HS can occur in any skin area that contains FPSUs.

• Symptoms:
  • Painful recurrent skin lesions present as tender erythematous nodules.
  • Pustules or abscesses
  • Draining skin sinuses
• Complications:
  • Scarring of the skin
  • Contractures
  • Fistulas in the anogenital region
  • Rarely, squamous cell carcinoma

Diagnosis

The diagnosis is based on a clinical exam. A history of the pattern of disease with recurrent deep skin abscesses and poor response to antibiotics is specific for HS.

• Clinical staging:
  • Stage I: 
    • Abscess formation 
    • No sinus tracts of scarring
  • Stage II: 
    • Recurrent abscesses
    • Single or multiple widely separated lesions with sinus tracts and scarring
  • Stage III: 
    • Diffuse involvement
    • Multiple sinus tracts and abscesses 
• Laboratory studies: 
  • Culture of superficial HS lesions for bacterial superinfection
  • Skin biopsy: only if diagnosis is unclear or to exclude other diseases
• Imaging: not necessary, but MRI can be helpful to diagnose HS of anogenital region specifically

Management

The key to management is early diagnosis and treatment.

• Conservative treatment:
  • Lifestyle modification: 
    • Weight loss
    • Smoking cessation
  • Warm compresses for painful skin lesions (dry better than wet)
• Medical management:
  • Antibiotics:
    • Clindamycin (both oral and topical)
    • Tetracyclines (doxycycline)
    • Amoxicillin/clavulanate
  • Retinoids: Isotretinoin is helpful.
  • Immunosuppressants/tumor necrosis factor alpha (TNFα) blockers:
    • Adalimumab
    • Infliximab 
    • Cyclosporine
• Surgical management for resistant disease:
  • Incision and drainage
  • Laying open of sinus tracts
  • Radial excision

Differential Diagnosis

• Carbuncles: a deeper skin infection involving hair follicles. Lesions present as painful, pus-filled, inflamed nodules on the skin. Carbuncles are commonly present in the back of the neck, shoulders, hips, and thighs due to higher friction and sweat production. Staphylococcus aureus is the main bacteria causing infection. Patients may have a fever. An infected carbuncle may resolve on its own with warm compresses or may require antibiotics.
• Lymphadenitis: an infection of lymph nodes presenting as tender, enlarged nodes that may be acute or chronic. Causes include bacterial and viral infection. The diagnosis requires a detailed history and examination. The most common cause of bilateral cervical adenitis is viral upper respiratory tract infection; tuberculosis is a consideration as well. For chronic cases, lab testing with CBC, erythrocyte sedimentation rate (ESR), culture, and serologic testing is recommended. Management is based on the underlying cause.
• Acne vulgaris: a common skin disorder characterized by the formation of papules, pustules, nodules, and/or cysts due to the inflammation of pilosebaceous units. Acne vulgaris can be mild or moderate-to-severe in presentation. The disorder may result in depression and anxiety in patients. The treatment includes counseling of patients along with antibiotics, retinoids (oral and topical), oral contraceptives, benzoyl peroxide, salicylic acid, and dapsone.
• Pilonidal disease: a suppurative condition of the skin and subcutaneous tissue resulting in intermittent bloody pus-filled discharge. Pilonidal disease can present as an abscess or draining sinus tracts. Diagnosis is mainly clinical. Excision is the standard definitive treatment of choice, and the recurrence rate is high. Risk factors include trauma, obesity, deep natal cleft, and positive family history. Antibiotics can be used in the presence of cellulitis, and surgery may be needed later for recurrent complicated lesions.