Crusted scabies - formerly known as Norwegian scabies - is a form of scabies that presents with more severe symptoms than classic scabies. It is characterized by large crusted lesions, generalized scales, thick hyperkeratosis, and contains an abundance of highly contagious mites. (1) This form of scabies is mostly found in patients with a debilitated immune system and/or loss of itch sensitivity. (2)
Patients present with hyperkeratosis of the skin in which mites proliferate. The scaly crusts may be found anywhere on the body but are most often overlooked behind the ears where they may appear similar to seborrhoeic dermatitis. Nail hyperkeratosis can be seen commonly. Crusted scabies can be localized to one area (e.g. the scalp, the face, or even just one finger, toe nail or sole) (3).
This form of scabies may not cause itching.
This form of scabies is characterised by heavy infestation of mites. The risk of transfer of infection via clothing, bedding, towels or upholstery is higher than for typical scabies infestations. Patients with minimal exposure (e.g. cleaning staff and laundry employees) should also be treated.
Bacterial secondary infection is common. There may be generalised lymphadenopathy (3).
Skin scrapings, examined under microscope, help confirm the diagnosis (3).
Differential diagnosis for crusted scabies includes an adverse drug reaction, psoriasis, contact dermatitis, ichthyosis, eczema, Darier's disease as well as seborrhoeic dermatitis (4).
Given the high parasite load, it is recommended that oral ivermectin be given in conjunction with topical permethrin until all scales and crusts are gone (5) Crusts may be dislodged and softened using keratolytic agents (e.g. 2% salicylic acid ointment) twice daily for 2-3 days. Treatment options for the scabies infestation include the combination of topical treatment with permethrin 5% and oral ivermectin (6).
People who have been even minimally exposed (e.g. cleaning staff and laundry employees) should be considered to have been exposed to infested persons, and should also be treated on account of the extremely contagious nature of crusted scabies. (7).
Reference:
1. Chandler D.J., Fuller L.C. A review of scabies: An infestation more than skin deep. Dermatology. 2019;235:79–90
2. Bhat S.A., Mounsey K.E., Liu X., Walton S.F. Host immune responses to the itch mite, Sarcoptes scabiei, in humans. Parasites Vectors. 2017;10:385
3. Cohen P.R. Classic and non-classic (surrepticius) scabies: Diagnostic and treatment considerations. Cureus. 2020;12:e7419
4. Talaga-Ćwiertnia K. Sarcoptes infestation. What is already known, and what is new about Scabies at the beginning of the third decade of the 21st century? Pathogens. 2021;10:868.
5. Currie BJ, McCarthy JS. Permethrin and ivermectin for scabies. N Engl J Med. 2010 Feb 25;362(8):717-25.
6. Palaniappan V., Gopinath H., Kaliaperumal K. Crusted scabies. Am. J. Trop. Med. Hyg. 2021;104:787–788
7. Seidelman J., Garza R.M., Smith C.M., Fowler V.G.J. More than a mite contagious: Crusted scabies. Am. J. Med. 2017;130:1042–1044.
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