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Scabies

Specialties > Dermatology

Background knowledge 🧠

Definition

  • Scabies is a contagious skin infestation caused by the mite Sarcoptes scabiei.
  • Mites burrow into the epidermis, leading to intense itching and skin rash.
  • Transmission occurs primarily through direct skin-to-skin contact.

Epidemiology

  • Global prevalence is estimated at over 200 million cases.
  • Higher incidence in overcrowded living conditions.
  • Affects all age groups but most common in children and young adults.
  • More prevalent in tropical and subtropical regions.

Aetiology and Pathophysiology

  • Caused by the mite Sarcoptes scabiei var. hominis.
  • Female mites burrow into the stratum corneum to lay eggs.
  • Eggs hatch into larvae within 3-4 days, continuing the cycle.
  • The intense itching is a result of a hypersensitivity reaction to mite proteins and feces.

Types

  • Classic Scabies: Most common form, characterized by generalized itching and a rash.
  • Nodular Scabies: Persistent nodules, particularly in the genital area.
  • Norwegian (Crusted) Scabies: Seen in immunocompromised individuals, with thick crusts containing large numbers of mites.
  • Scalp Scabies: Less common, often seen in infants and the elderly.

Clinical Features 🌡️

Symptoms

  • Severe itching, especially at night.
  • Rash, often appearing as small red papules.
  • Burrow marks, thin greyish lines on the skin.
  • Possible secondary infection due to scratching.

Signs

  • Burrows: Thin, wavy grey lines on the skin, particularly in web spaces of fingers, wrists, and elbows.
  • Erythematous papules: Commonly found on the hands, feet, and genital areas.
  • Excoriations and secondary eczematization.
  • Crusted lesions in severe cases (Norwegian Scabies).
  • Nodules may persist after treatment (Nodular Scabies).

Investigations 🧪

Tests

  • Clinical diagnosis primarily based on history and examination.
  • Skin scraping: Mites, eggs, or fecal pellets can be identified microscopically.
  • Dermoscopy: Visualization of burrows and mite in vivo.
  • Biopsy: Rarely needed, but can show characteristic features.

Management 🥼

Management

  • Topical permethrin 5% cream: First-line treatment, applied to entire body and washed off after 8-12 hours.
  • Oral ivermectin: For severe cases or where topical treatment fails.
  • Treat household members and close contacts simultaneously.
  • Wash clothing, bedding, and towels in hot water and dry on high heat.
  • Avoid close contact until treatment is complete.

Complications

  • Secondary bacterial infection: Commonly due to scratching (e.g., impetigo).
  • Post-scabetic nodules: Can persist for weeks to months after treatment.
  • Eczema: Due to chronic scratching and skin irritation.
  • Social stigma and psychological distress.
  • Norwegian (crusted) scabies: Can lead to severe systemic illness in immunocompromised patients.

Prognosis

  • Excellent with proper treatment.
  • Symptoms usually resolve within 2-4 weeks.
  • Recurrence can occur if treatment is incomplete or re-exposure happens.

Key Points

  • Scabies is a common and highly contagious condition.
  • Prompt diagnosis and treatment are essential to prevent spread.
  • Treat all close contacts to avoid reinfection.
  • Be aware of atypical presentations, particularly in immunocompromised patients.

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Dermatology