Myth: Bedtime exacerbation of itching is pathognomonic for scabies.

Reality: Virtually all pruritic conditions worsen when the patient lies down to sleep. During the day, patients are distracted from the itching, so it does not become a problem until their only task is getting to sleep.

Myth: Presumptive diagnosis and treatment of scabies is reasonable in primary care.

Reality: In many primary-care settings, scabies is diagnosed and treated presumptively without consideration for other diagnostic possibilities. This can cause problems, not only for the patient but eventually for the patient’s circle of contacts. When treatment for scabies fails in a patient with one of the differential conditions, the person feels compelled to consult another provider who, most likely, will try another empirical treatment. It is best for everyone involved if a specific diagnosis can be obtained, and in the case of scabies, that means performing a scabies scrape.

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Myth: Scabies scrapes are difficult and time-consuming to perform.

Reality: This is a common myth in primary care. Often, scabies scrapes aren’t performed because clinicians don’t know how to do them or they don’t see the necessity. In truth, performing and reading scrapes is simple and no less important than obtaining an x-ray to rule out pneumonia or urinalysis to confirm a bladder infection.

This procedure takes a maximum of four to five minutes. When you find what you’re looking for, you can return to the exam room and tell your patient what he or she has with complete confidence.

Myth: Scabies is often resistant to treatment.

Reality: While lindane is no longer uniformly effective for treating scabies, permethrin (Elimite) is effective when used as directed. Treatment failure is usually the result of how the treatment was performed rather than what medication was used. As previously mentioned, the single most common cause of treatment failure is the fact that the patient never had scabies in the first place. When the patient actually is diagnosed with recurrent scabies, attention must be given to the treatment details outlined below.

Myth: Environmental cleanup is a crucial component of treatment.

Reality: When most patients hear the word “scabies,” their only frame of reference is fleas. In contrast to fleas, which can live in or on such inanimate objects as carpets, scabies mites will only survive for a short time off the human body (usually less than two days). They typically do not lay eggs on or reside in inanimate objects, so even though cleaning the surrounding environment makes some sense, it is more important to identify the source of the infestation and thoroughly treat all contacts.

Clinicians should emphasize treatment over environmental cleanup because many patients pay so much attention to steam-cleaning their entire house that they neglect treatment issues. It should be noted that dealing with scabies in an institutional setting (nursing home, mental hospital, etc.) requires increased emphasis on environmental cleanup because the exposure time is greater.

When cleaning the environment, make sure to change the bedding, towels, and sleepwear; vacuum the couch; and place any stuffed toys in the freezer for a week or two.

Myth: Adequate treatment results in the immediate cessation of symptoms.

Reality: Treatment regimens must be followed specifically. All contacts should be treated twice, at the same time, seven days apart (to allow any eggs to hatch). During this period, suspicious contacts should be avoided (especially children and sexual partners). Permethrin should be applied to every skin surface below the neck, including under freshly cleaned fingernails. This site is often overlooked, and scratching can cause the condition to spread. On babies, unlike older children and adults, scabies can infest scalps and soles, so these areas must also be treated.

Unfortunately, the pruritus associated with scabies can and often does persist for weeks following treatment, although the intensity does decrease with time. Patients frequently call back within a week or two to complain about the itching, so it’s important to be completely certain about the diagnosis. Without certainty, treatment is often changed, usually to a steroid, which will make scabies worse, if in fact the patient has it. It is important to educate the patient about the likelihood of continuing symptoms.

Mr. Monroe is a physician assistant specializing in dermatology at Springer Clinic in Tulsa, Okla., and founder of the Society of Dermatology Physician Assistants.