Scabies

Scabies: Overview - Itchy Tiny Terrors

• Definition: Intensely pruritic skin infestation by Sarcoptes scabiei var. hominis (human itch mite).
• Lifecycle: Female mite burrows in epidermis, lays eggs. Larvae hatch (3-4 days), mature to adults (10-14 days).
• Transmission: Primarily prolonged skin-to-skin contact. Fomites: less common (classic), significant (crusted).
• Incubation Period:
  • Non-sensitized (1st infection): 2-6 weeks.
  • Sensitized (re-infestation): 1-4 days.

⭐ Crusted scabies is highly contagious due to a massive mite burden (up to millions of mites), often in immunocompromised individuals anergic to the mite antigens, leading to minimal itching despite high parasite load.

Scabies: Clinical Features - Burrowing Blues

• Cardinal Symptom: Intense pruritus, classically worse at night.

  ⭐ Intense nocturnal pruritus ("wake-up sign") is a hallmark of scabies, often disrupting sleep.

• Characteristic Lesions:
  • Burrows (pathognomonic): Greyish/skin-colored, serpiginous lines.
  • Papules, vesicles, pustules, nodules, excoriations.
• Distribution:
  • Common sites: Finger webs, wrists (flexor), axillae, elbows, beltline, buttocks, genitalia (males), areolae (females).
  • Head/neck/palms/soles usually spared in adults; may be involved in infants, elderly, or immunocompromised.
  • 📌 ITCHING SITES: Interdigital, Trunk (beltline), Creases (axillae, elbow), Hands/wrists, Insteps, Navel, Genitalia, Scapula/Shoulder.
• Special Types:
  • Crusted (Norwegian) Scabies: Hyperkeratotic plaques, ↑↑ mite load (millions), highly contagious. Often in immunocompromised/elderly; pruritus may be minimal initially.
  • Nodular Scabies: Persistent, itchy, reddish-brown nodules (e.g., groin, axillae, buttocks); a hypersensitivity reaction.
  • Bullous Scabies: Resembles bullous pemphigoid; blisters present.
  • Scabies Incognito: Altered appearance due to topical steroid use, masking typical signs.

Scabies: Diagnosis - Mite Spotting Mission

• Clinical dx: History (pruritus, contacts), lesion pattern.
• Skin scraping: #15 blade, mineral oil; find mites, eggs, scybala. Variable sensitivity.
• Dermoscopy: "Delta wing" sign (mite's pigmented anterior), "jetliner with contrail" (mite & burrow).
• Adhesive tape test: Alternative, esp. children.
• Biopsy (rare): Mites in stratum corneum, eosinophils.

⭐ Negative scraping doesn't rule out scabies; mite count can be low (avg 10-15).

• DDx: Eczema, insect bites, papular urticaria, dermatitis herpetiformis.

Scabies: Treatment - Eviction Notice

• Goals: Eradicate mites, manage pruritus, prevent transmission.
• Topical (1st line): Permethrin 5% cream (DOC). Neck down, 8-14 hrs, repeat 1 wk. 📌 Permethrin is Perfect.
• Oral: Ivermectin (200 mcg/kg single dose, repeat 1-2 wks). For crusted, outbreaks, non-compliant. 📌 Ivermectin is Internal.
• Crusted Scabies: Combo topical + oral Ivermectin (multiple doses), keratolytics.
• Special Pop: Infants >2m, pregnant/lactating: Permethrin 5%.
• Adjuncts:
  • Antihistamines (pruritus), mild topical corticosteroids (post-scabetic dermatitis).
  • Treat contacts (simultaneously, even asymptomatic).
  • Environment: Wash items >50°C or seal ≥72 hrs.

⭐ Post-scabetic pruritus (2-4 wks) common after mite eradication due to hypersensitivity; not treatment failure.

Scabies: Complications & Prevention - Staying Clear & Calm

• Complications:
  • Bacterial superinfection (impetigo, cellulitis; risk PSGN, ARF)
  • Post-scabetic pruritus, nodular scabies
  • Scabies incognito (steroid misuse)
• Prevention:
  • Prompt treatment: index case & all contacts
  • Hot wash/dry linens, clothing
  • Patient education

⭐ Secondary bacterial infections are common, serious, and can lead to systemic illness.

High‑Yield Points - ⚡ Biggest Takeaways

• Caused by mite Sarcoptes scabiei var. hominis.
• Intense nocturnal pruritus is the hallmark symptom.
• Burrows are pathognomonic; common in interdigital webs, wrists, axillae, genitals.
• Diagnosis: Microscopy of skin scrapings for mites, eggs, or scybala.
• Treatment: Permethrin 5% cream (topical); oral Ivermectin for severe/crusted scabies.
• Crusted (Norwegian) scabies: Seen in immunocompromised patients; highly contagious with numerous mites.
• Treat all household members and close contacts simultaneously to prevent re-infestation_._