Crusted scabies is a severe type of scabies. People with crusted scabies have scabies mites and eggs within thick crusts of skin. It is most likely to affect the hands, feet, elbows, and knees.
People may also refer to crusted scabies as Norwegian scabies.
In this article, we look at what crusted scabies are, its causes, symptoms, and treatment options, and when to see a doctor.
Crusted scabies is a severe infestation of scabies mites and eggs in the skin. The scabies mite, Sarcoptes scabiei var hominis, is a microscopic mite also known as the human itch mite.
Scabies mites are only able to reproduce on human skin. The female scabies mite burrows into the top layer of skin and lays its eggs.
Most people with scabies have an infection of roughly 10–20 mites. People with crusted scabies may have as many as 4,000 mites per gram of skin or an infection of more than 1 million mites.
People with crusted scabies may also experience different symptoms compared to people with regular scabies. People with crusted scabies may not experience itching or a rash, which occurs in regular scabies.
Scabies is contagious, and crusted scabies is especially so because it involves a larger infestation of mites. Crusted skin with mites can also fall off the body. This allows the mites to live for up to one week with food and protection and without the need for human contact.
People can get scabies from contact with someone who has scabies. Crusted scabies can pass on through skin-to-skin contact, as well as through clothing, bedding, or furniture.
There is currently no known cause for someone developing crusted scabies rather than the less severe form. There may be a link between crusted scabies and higher levels of disease-fighting white blood cells, along with the antibodies IgE and IgG.
Two types of white blood cells, called lymphocytes and eosinophils, invade the dermis layer of the skin. A person also has a higher level of lymphocytes than usual.
Who is most likely to get crusted scabies?
Some people have a higher risk of crusted scabies. Risk factors include:
- older age
- Down syndrome
- a weakened immune system
- Hansen’s disease (leprosy)
- systemic lupus erythematosus (SLE)
- long-term use of corticosteroids or immunosuppressants
People in living in institutional settings may also have a higher risk of scabies in general.
Scabies is common in nursing homes and extended-care facilities in the United States. This is because frequent skin-to-skin contact between staff and residents can cause scabies to spread quickly.
Early signs of crusted scabies include red patches on the skin that lack a defined edge. These patches later develop into thick plaques.
Common areas where crusted scabies may appear on the body are:
- between the fingers
- underneath the nails, or in the nail beds, which may cause the nail to split
- spread over the palms of the hands and soles of the feet
People may not have the itching or rash that usually appears with scabies. People may have slight itching, but this is not always present in crusted scabies.
People will need to treat crusted scabies quickly to prevent spreading scabies to others. Treatment may include oral or topical medication or a combination of both. Those medications include oral Ivermectin, a medication to treat parasitic infections, and topical insecticides or scabicides such as Permethrin, benzyl benzoate, or Crotamiton.
People may also use keratolytic creams, which break down the protein keratin. These help to soften the thick, scaly plaques. People may use 5-10% salicylic acid in sorbolene cream or 5% lactic acid and 10% urea in sorbolene cream.
People may need to remove scaly patches of skin before applying treatments in order to help topical insecticides penetrate deeper into the skin.
People may need treatment for several weeks or longer until the infestation is gone. People may need further treatment if they still have signs of a scabies infection after a month of treatment.
Family members, or people in close contact with anyone with crusted scabies, will also need treatment with a topical scabicide.
In some cases, crusted scabies may cause complications. Potential complications include:
- infestation of scabies among close contacts
- secondary bacterial infection
- reinfestation of scabies
- higher risk of sepsis in older adults with crusted scabies compared to regular scabies
People will need to see a doctor to diagnose crusted scabies. A doctor will examine the skin with a microscope to check for burrows, mites, and eggs.
Doctors may also use a technique called reflectance confocal microscopy (RCM). RCM is a non-invasive imaging method of examining the epidermis and dermis of the skin.
Infants and people who are pregnant may need a biopsy to confirm the diagnosis and ensure treatment is necessary.
Crusted scabies is a treatable condition. It is important to continue treatment until no signs of infection are present in order to prevent reinfestation.
People living in institutions, or those with a weakened immune system, may be at higher risk of reinfestation. Education about crusted scabies and regular follow-ups are important in helping to prevent reinfestation.
The risk of sepsis, which can be life-threatening, is higher in older adults with crusted scabies compared to those with the common type of scabies.
People will need to contact their doctor if they have crusted scabies. Doctors who specialize in skin conditions, such as a dermatologist or infectious disease doctor, may treat and monitor people with crusted scabies, and any of their close contacts.
People may need to have treatment in hospital or other care facility. People will need to be in a private room, to avoid spreading scabies to others.
Crusted scabies is a severe type of scabies. People with crusted scabies have much larger amounts of scabies mites and eggs present in their skin compared to regular scabies.
Crusted scabies is very contagious. It can spread from skin-to-skin contact, as well as through contaminated clothing, bedding, or furniture.
Crusted scabies does not usually cause a rash or itching, but can cause red patches and scaly plaques on the skin. It often appears around the hands and fingers, knees, elbows, and soles of the feet.
People will need to see a doctor for treatment of crusted scabies. Treatment may include oral and topical medication. Both are effective treatments for crusted scabies.