Classic and Non-classic (Surrepticius) Scabies: Diagnostic and Treatment Considerations

Abstract

The morphology of scabies, a mite infestation of worldwide proportion, is characterized by a variety of cutaneous lesions. Patients with classic scabies present with characteristic burrows often located on the web spaces of the fingers and toes. Scabies surrepticius refers to the non-classic atypical presentation of scabies; establishing the diagnosis of scabies in these individuals can be difficult. To facilitate the diagnosis of scabies, criteria have been proposed by the International Alliance for the Control of Scabies (IACS). These criteria are intended for scabies research; however, they can be utilized by clinicians to establish either a confirmed diagnosis, a clinical diagnosis or a suspected diagnosis of scabies. Visualization of mites, eggs or feces is necessary for a confirmed diagnosis of scabies. A clinical diagnosis can be established by observation of either genital lesions in men or burrows or classically distributed classical lesions in individuals with two historic features: pruritus and close contact with an individual who itches and has classically distributed classical scabetic lesions. The clinical features and management of a woman residing in an assisted living environment with a confirmed diagnosis of scabies and a man with a clinical diagnosis of scabies are described. The criteria for the suspected diagnosis of scabies require either one historic feature and typical lesions in a typical distribution or both historic features and the presence of atypical lesions or an atypical distribution of the skin lesions. Once the diagnosis of scabies is established, not only the patient but also close contacts should receive treatment with either a topical medication (such as permethrin 5% cream) or a systemic drug (ivermectin) or both. The number and frequency of treatments are variable; classic scabies typically is managed with a total of two treatments performed weekly to biweekly. Patients with crusted scabies usually require multiple topical and oral antiscabetic treatments in addition to topical keratolytic therapy. Bacterial impetiginization or infection (most commonly by Staphylococcus aureus or Streptococcus pyogenes) can complicate scabies infestation and potentially result in cellulitis, abscess, sepsis, rheumatic fever, rheumatic heart disease and post-streptococcal glomerulonephritis; therefore, in some patients, systemic antimicrobial therapy may be necessary in addition to scabies-directed treatment. In addition to systemic antihistamines, oral and/or topical corticosteroids may be used to provide symptomatic pruritus relief once the diagnosis of scabies has been established and mite-directed treatment has been initiated. The clinician should consider several potential causes (such as inadequate treatment, reinfection, mite resistance, delusions of parasitosis and the development of a new non-scabetic dermatosis) in scabies patients who fail to respond to treatment with a topical or oral scabicide therapy.