Diagnosis

Scabies

Etiology

Cause [2ir]

• Infestation of the parasitic mite Sarcoptes scabiei hominis (8-legged arthropods measuring up to 0.45 × 0.35 mm)

Pathophysiology

1. Transmission of scabies is predominantly through direct skin-to-skin contact

2. Eggs -> Larvae -> Nymps -> Adult female

3. Proteolytic enzymes in the saliva lyses the stratum corneum

4. This enables intraepidermal tunnel/burrow (elevations in the superficial epidermis)

5. The mite ingest intercellular fluid that accumulates within the tunnel and lay eggs

6. Does not penetrate deeper than the superficial layer of the epidermis

7. Able to live on bedding, clothes, or other surfaces at room temperature for 2-3 days

8. Mite antigens trigger a delayed type IV hypersensitivity reaction in the dermis:

   • Intense nocturnal pruritus

   • Skin lesions: excoriated papules, eczematous or lichenified plaques, nodules and pathognomonic burrows (short, wavy white lines with a vesicle or erosion at the distal end that harbors the mite)

Risk factors [ttm]

• Travel

• Younger age

• Low Socioeconomic status:

  • Refugees, asylum seekers

  • Lack of drinking water

  • Lack of appropriate hygiene, irregular use of showers

  • Illiteracy

  • Low family income, poor housing

  • Sharing clothes and towels

Complications [2ir]

• Insomnia

• Secondary bacterial infection (impetigo)

• Superimposed cellulitis/abscess

• Poststreptococcal glomerulonephritis

Epidemiology

Incidence per 100.000 [vk7][sko][vzb][nhd][4ee][sms][fpn]

Approach

• Dermatoscope: Pruritic rash and characteristic linear burrows

• Light microscopy of skin scraping to identify mites, larvae, ova, or scybala (feces)

• Biopsy

• PCR

Diagnostic criteria [2ir]

1. Suspected scabies: Characteristic rash and intense (nocturnal) pruritus

2. Clinical scabies: The above, plus visible burrows

3. Confirmed scabies: Previous criteria, plus visualization of mites, eggs, or feces

Treatment

1. Scabicidal agent: [ttm][2ir]

   • Permethrin (topical 5% cream) applied once weekly for 2 weeks

   • If age > 2 months: Sulfur ointment (5%-10%)

   • Ivermectin (oral) 200 μg/kg repeated after 14 days

   • Lindane 1% (neurotoxicity and hematologic sideeffects)

2. In case of secondary infection: Antimicrobial agent

3. Pruritus: Oral antihistamine (Atarax)

Differential diagnoses

Acropustulosis of infancy, Bullous pemphigoid, Chickenpox, Contact dermatitis, Dermatitis artefacta, Dermatitis herpetiformis, Dermatographism, Drug eruptions, Eczema, Erythroderma, Folliculitis, Gianotti-Crosti syndrome, Ichthyosis vulgaris, Impetigo, Insect Bite, Kyrle disease, Langerhans cell histiocytosis, Leukemia, Lice, Lichen planus, Lymphoma, Mastocytosis, Necrotizing vasculitis, Parapsoriasis, Parasitic infestations, Pemphigus vulgaris, Prurigo nodularis, Psoriasis, Seabathers eruption, Syphilis, Systemic lupus erythematosus, Urticaria