Scabies crustosa (Norwegica)

Synonyms

Crusted scabies; scabies Norwegica; Norwegian scabies.

Epidemiology

Approximately 300 million individuals are affected worldwide each year with scabies. Risk factors for developing crusted scabies include immune deficiency, increased age, dementia, long term immunosuppression, past history of leprosy, special environmental factors (prison), misdiagnosed eczema or prosiasis. Population on risk: aboriginal communities in northern Australia.

Definition

Highly contagious infestation with Sarcoptes scabiei var hominis, mostly seen in immuno compromised patients and showing unhindered proliferation of mites. No special aetiopathogenic or semantic relationship to Norway.

Aetiology & Pathogenesis

Impaired immune status may lead to unlimited spread of mites. Sarcoptes scabiei var. hominis is a human ectoparasite with marked host specificity. Human-to-human transmission occurs with close personal contact, sometimes via clothing or bedding. Female mites (0.3-0.5 mm) dig a burrow in the stratum corneum of the epidermis to lay their eggs; sexually mature mites develop in 3 weeks. Immunologic reaction to mite antigens causes inflammation and pruritus.

Signs & Symptoms

Erythematous patches develop into thick scaly hyperkeratotic, psoriasiform, fissured, and yellow-to-brown crusted plaques. Unlike classical scabies, pruritus is either mild or absent.

Localisation

Total body. Prediliction sites: fingers, under the nails, and diffusely over palms and soles; elbows and knees.

Classification

A grading scale has been proposed, based on 4 clinical symptoms: the distribution and extent of crusting; the depth of crusting; the degree of skin cracking and pyoderma; and the number of previous episodes.

Laboratory & other workups

Investigation of the immune status. Identification of the mite, its eggs, or scybala (feces) under the dermatoscope or microscope. Blood tests (eosinophilia, anti-nuclear antibodies).

Dermatopathology

Usually not necessary. Acanthosis and hyperkeratosis. Marked thickening of the stratum corneum, containing numerous parasites. Polariscopic examination (birefringence) may be a helpful clue for the visualization of mites and scybala.

Course

Risk of reinfection due to impaired immune status; increased mortality rate.

Complications

Contamination of contact persons and secondary bacterial infection, due to scratching and fissuring of the skin. Septicaemia with increased mortality rate.

Diagnosis

Clinical feature. Identification of mites, eggs or scybala (feces) by dermoscopic, skin scraping or de-roofing burrow with scalpel blade, microscopic examination or reflectance confocal microscopy of burrows.

Differential diagnosis

Pruritic dermatoses, prurigo, psoriasis, hyperkeratotic eczema.

Prevention & Therapy

Prevention and topical treatment like in conventional scabies.

Systemic treatment: Ivermectin 200 μg/kg (adults and children over 14 kg), together with a fatty meal to improve absorption.

Special

Highly contagious.

10.5.2 Scabies crustosa (Norwegica)