Scabies Surrepticius (Presenting as Crusted—Norwegian—Scabies, Scalp Scabies, an

Dear Editor:

I read with interest the excellent report by Zhang et al.1of a 55-year-old woman with Norwegian scabies(which is also referred to as crusted scabies) that masqueraded as scalp seborrheic dermatitis for 5 months until the correct diagnosis was established. The authors attributed her immunosuppressed state—which accounted not only for the crusted scabies but also its location on her scalp in addition to other body areas—to a chronic hepatitis C infection. Her mite infestation also had a component of scabies incognito from the application of high-potency topical corticosteroids (0.05% fluticasone propionate cream and 0.1% halcinonide solution) for 5 months.1

Individuals with a classic scabies infestation present with pruritus and pathognomonic burrows typically found on the web spaces of the fingers and toes.2-3However, the lesion morphology or location or both are atypical in patients with non-classic scabies for which the term scabies surrepticius has been introduced and acknowledged.4-6Indeed,scabies surrepticius encompasses not only crusted scabies, scalp scabies and scabies incognito (in which the patient has been treated with systemic and/or topical corticosteroids resulting in the mite-associated lesion to be atypical) but also bullous scabies (which clinically and pathologically mimics bullous pemphigoid), nodular scabies and other vairants of scabies that mimic dermatitis herpetiformis, ecchymoses, Langerhans cell histiocytosis,pityriasis rosea, prurigo nodularis, systemic lupus erythematosus, urticaria, and urticaria pigmentosis.4

As emphasized by Zhang et al.,1immunosuppression is a characteristic feature of individuals with crusted scabies.In addition, disease-associated or iatrogenic immunosuppression is also common in scabies patients with miteassociated scalp lesions.7Chronic hepatitis C infection can be added to the conditions; the other conditions include AIDS, dermatomyositis, leukemia, lymphoma, systemic lupus erythematosus, and trisomy 21.4

The management of scabies requires treatment that not only eliminate the mites but also is ovicidal. In patients with crusted scabies,treatment to eliminate the cutaneous scaling is also necessary. Zhang et al.1succinctly summarize the therapeutic interventions to treat scabies that are available in China;in the United States of America,the standard approach to scabies treatment would likely include repetitive courses of topical permethrin 5%cream and oral ivermectin.3,8

Zhang et al.1commented that their patient’s scalp lesions persisted after several treatments. Recurrence or persistence of scabies infestation is a common problem.It can result from repeat infestation from non-treated scabies-infested family members who are in close contact with the patient.3,8

Alternatively, chronic mite infestation can result from inadequate topical application of the scabicide. Many older patients cannot reach their toes or their entire back.In addition,many individuals do not apply the medication to “mite sanctuary sites” such as beneath all of their fingernails and toenails, to their umbilicus, and to their perianal area.8

To ensure that the scabicide is appropriately applied, it has recently been suggested that the patient return to the doctor’s office or a specialized treatment center to apply the medication. The presence of mites above the neck is traditionally not suspected in immunocompetent individuals. However, it has also been proposed that topical scabicides be applied to the face and scalp of not only immunosuppressed patients but also individuals with a presumed normal immune system.8

In conclusion,scabies surrepticius is the new nomenclature for mite infestations with an atypical morphologic appearance. Immunosuppression—either disease-related or iatrogenic—predisposes those individuals to variants of scabies surrepticius such as crusted scabies, scalp scabies and scabies incognito. Scabies management requires repeated adequate systemic and/or topical treatment not only for the patient but also for family members and other individuals who have had contact with the patient; in addition, empiric topical application of the scabicide above the neck should be considered for all patients with scabies mite infestation regardless of whether they are immunosuppressed or immunocompetent.

Philip R. Cohen

San Diego Family Dermatology, National City, CA,USA; Touro University California College of Osteopathic Medicine, Vallejo, CA, USA.

Email: mitehead@gmail.com