The original diagnosis in this case was correct—Lyme disease (erythema chronicum migrans)—but unfortunately, the treatment was inadequate. Initially, this patient received a single dose of doxycycline 200 mg po, which is the appropriate preventative remedy when a deer tick has been attached for at least 36 hours and treatment can be initiated within 72 hours of tick removal. However, deer ticks, especially nymphs, are very small and their presence can go unnoticed, leading patients to guess (sometimes incorrectly) at the length of time a tick has been attached.
In this case, when the patient and his wife thought about it a bit more, they indicated that the tick may have been attached for several days before they removed it and went to see the PCP. Had the PCP known the tick had been attached longer, she would have advised watchful waiting and observation for signs and symptoms of Lyme disease.
Originally described in cases from Lyme, Connecticut, Lyme disease is now endemic to the northeastern United States from Maine to Virginia, and from the upper midwest to Minnesota. Laboratory diagnosis can be made by a 2-tiered serologic screening and confirmation with an enzyme-linked assay, followed by a western blot for positive or equivocal screening tests.
In 2019, the most recent year of reported Centers for Disease Control and Prevention (CDC) surveillance data, Maine recorded the highest incidence rate of Lyme disease.1 In 70% to 80% of cases, an expanding horizon of infection creates the characteristic targetoid pink patch centered on the site of the tick bite.2
If there is a targetoid rash present in a patient from an endemic area, the CDC recommends empiric therapy with doxycycline 100 mg po bid for 10 to 14 days.3 (Worth noting: Patches may appear rather small in diameter, as was true in this case, or may be many centimeters in size and mimic cellulitis.) Alternative regimens for early localized disease include amoxicillin 500 mg po qid for pregnant patients, and cefuroxime 500 mg bid daily for 14 days for patients who are allergic to doxycycline.
Once treatment has been initiated, it’s important to monitor patients for any worsening symptoms, including fever and weakness, as these may be an indication of treatment failure or co-occurrence of anaplasmosis, ehrlichiosis, or babesiosis. In this case, the patient was prescribed doxycycline 100 mg bid for 14 days without any further signs or symptoms.
Text courtesy of Jonathan Karnes, MD, medical director, MDFMR Dermatology Services, Augusta, ME. Photos courtesy of Jonathan Karnes, MD (copyright retained).