Scabies is not a new disease. Aristotle referred to it as “lice in the flesh” 2500 years ago. About 300 million cases occur worldwide each year. Emergency physicians are no strangers to this disease, and are often expert in recognizing and diagnosing scabies. But now there is a new weapon against this mighty mite that many EPs aren't too familiar with, something definitely worth adding to your bag of tricks.
Scabies is an obligate parasitic infection of humans caused by the mite Sarcoptes scabiei variety hominis. Although it can be classified as a sexually transmitted disease, infection typically occurs as a result of nonsexual and prolonged direct skin contact. Transient skin contact such as a handshake is unlikely to result in transmission of disease, although fomite transmission (clothing, bedding, mattresses) can occur.
Scabies is clinically manifested by intense pruritus, usually worse at night. The rash consists of burrows and pustules often found between fingers, the flexor surfaces of the forearms, the groin, and the axillae. The incubation period averages four weeks, but can be as long as 10 weeks. Because the itching from scabies is caused by an allergic reaction to the mite and its feces, recurrent infections in sensitized individuals can become symptomatic much sooner.
A definitive diagnosis of scabies requires the identification of mites, eggs, or mite pellets. Because the average human case has only 10 to 15 mites, the yield of scrapings can be extremely low. (Dermatol Ther 2009;22;466.) The diagnosis is most commonly made on clinical grounds alone.
Crusted scabies, historically first reported in patients from Norway, is an extremely severe form of scabies often seen in elderly patients, those with cognitive deficiency, and those with immunocompromise. Because these patients may carry an unusually heavy mite burden, it is a much more contagious variant of scabies. It is also much more likely to be misdiagnosed or even go unnoticed because afflicted patients often cannot communicate their complaints.
Permethrin and Ivermectin for Scabies
Currie BJ, McCarthy JS
N Engl J Med
Ivermectin was originally developed in the 1970s as a veterinary drug to treat parasites. It is still used extensively to treat demodectic and sarcoptic mange (caused by Sarcoptes scabiei canis). Since the mid-80s, ivermectin has been used worldwide to treat millions of human cases of onchocerciasis (river blindness) and strongyloidiasis, presently the only two FDA approved indications for this medication.
This article discusses in detail two therapeutic options for this ancient malady: topical permethrin and oral ivermectin.
There is a scarcity of high-quality studies comparing various therapies for scabies. A recent Cochrane review of multiple small trials concluded that topical permethrin was a more effective treatment for scabies than either oral ivermectin or other topical therapies (crotamiton, lindane, benzyl benzoate).
Only one study is available in the literature comparing oral ivermectin with topical permethrin. (J Am Acad Dermatol 2000;42[2 Pt 1]:236.) This study noted a cure rate of only 70 percent with single-dose oral ivermectin versus a 98 percent cure rate with a single application of topical permethrin. If a second dose of ivermectin was given one to two weeks after the first, however, the cure rate increased to 95 percent. Experts hypothesized that the lower efficacy of single-dose ivermectin was because it does not kill unhatched eggs, although other small studies have reported much higher cure rates (93%) with single-dose ivermectin. (Trop Doct 2001;31:15.)
Despite which therapy is used, many experts recommend repeating treatment one week later. Crusted scabies is often treated with topical permethrin and oral ivermectin simultaneously. The ivermectin dose most commonly studied is 0.2 mg/kg (about 14 mg to 16 mg per average-sized adult). According to the article, the average wholesale price for either treatment is about the same.
Ivermectin is not FDA-approved in the United States, United Kingdom, or Australia for treating scabies, but off-label use is increasing due to cost, convenience, and ease of administration. Ivermectin has been approved in France for scabies since 2001. Ivermectin is not recommended for children under 5 or in pregnant or nursing women.
Although not usually considered a dangerous or deadly disease, misdiagnosis can have a widespread effect on other patients. One study found that the ED only recognized 35 percent of proven scabies cases in patients admitted to the hospital. In another case report, an HIV-patient with undiagnosed crusted scabies resulted in the preemptive treatment of a total of 1659 individuals. (Infect Control Hosp Epidemiol 2009;30:354.) Another outbreak in a community hospital subacute unit involved hundreds of employees, patients, and their relatives. After the initial outbreak, cases kept recurring for more than two years until the local health department finally determined it to be a case of ongoing mass scabies hysteria!
Ivermectin should be a new addition to your ED armamentarium. When the diagnosis is in doubt, err on the side of treating, especially if your patients can't verbalize the history of their rash very well. If you want to find an easy way to become infamous at your institution, miss this diagnosis in a patient you admit, and see how loud this mighty mite can roar!
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AAEM Creates Master's Designation
The American Academy of Emergency Medicine has created a designation of Master of the American Academy of Emergency Medicine (MAAEM), with the first recipients set to be introduced at its annual Scientific Assembly next February. The new title will recognize a group of senior AAEM fellows who have demonstrated a career of service to the academy as well as work in teaching, research, volunteering, or health policy advocacy. Those honored as masters will be authorized to use the MAAEM title for as long as their AAEM membership remains current.
© 2011 Lippincott Williams & Wilkins, Inc.