Master the board step 3

Master the Boards: USMLE Step 3
Diagnostic Testing
Scabies is confirmed by scraping out the organism after mineral oil is applied
to a burrow.
Treatment
Treatment is with permethrin. Lindane has equal efficacy but greater toxicity;
thus, it is not the best initial therapy. Scabies, particularly Norwegian scabies,
can be treated with ivermectin orally.
Pediculosis (Lice and Crabs)
Pediculosis tends to include the head and is easily transmitted by sharing
hats and hairbrushes. Both organisms have an enormously high rate of transmission
through sexual contact, with 90 percent transmission from a single
contact. They are sometimes rust colored from their ingestion of blood.
Diagnostic Testing
Because pediculosis is caused by a much larger organism, scraping is not necessary.
The organisms can readily be seen attached to hair-bearing areas,
particularly under magnification.
Treatment
As with scabies, treatment is with permethrin. Lindane has equal efficacy but
greater toxicity; thus, it is not the best initial therapy. Pediculosis can be treated
with over-the-counter pyrethrins.
Lyme Disease
More than 85 percent of patients who have Lyme disease develop a rash. The
rash must be erythematous with central clearing and be at least 5 cm in
diameter. It usually occurs 7–10 days after the tick bite.
This rash is so characteristic of Lyme that it is more important than serological
testing in terms of confirming a diagnosis. If the rash is described, then
go straight to therapy with oral doxycycline, amoxicillin, or cefuroxime.
Without therapy,
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two-thirds of these patients will develop joint disease.
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a smaller number will develop neurological or cardiac disorders.
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