Question of the Week # 5

A 30 y/o pregnant woman has a one week history of a slowly enlarging red lesion on her right thigh. She reports having gone on a camping trip about 3 weeks ago and now recalls that she removed a tick from the site of the lesion. An ELISA test is negative for Lymes. Upon further questioning, she also reports contact with poison Ivy like  bushes during the same camping trip :

Archer USMLE Step 3 Questions

What is the next step?
A. Re-assurance
B. Ampicillin
C. Doxycycline
D. Western blot testing
E. Topical Corticosteroid
Copy Rights: USMLEGalaxy, LLC

15 Responses

  1. b

  2. B.

  3. B

  4. B ampicillin the elisa test is in the window period, it is not yet positive
    I prefer to treat the patient to prevent cardiac or neuro complications

  5. I assumed it is B also, but why no reply from Archer yet?

    Dr Red, can you confirm that the answer here is B?

  6. Ans. B

    Ampicillin ( Ans.B) is the most appropriate antibiotic for this pregnant woman with early stage Lymes disease. The patient has erythema chronicum migrans which is pathognomonic of early lymes disease. ELISA may be negative in early stage LYME disease and diagnosis must be based on clinical history. No further testing is necessary in the presence of such strong clinical history.

    Ans. A is inappropriate and not treating lyme disease can be lethal to the patient.

    Ans. C is an appropriate first choice for non pregnant patients with lyme disease. Doxycycline is classified as pregnancy category D. Tetracycline exposure during the second or third trimester can cause permanent discoloration of the teeth.

    Ans. D is incorrect. Western blot is only used to confirm a positive ELISA test because ELISA is associated with a high rate of false positive results. In the absence of strong clinical suspicion, both ELISA and Western blot must be positive in order to diagnose lyme disease. Such testing is especially useful when someone is suspected to have late lyme disease manifestations. ELISA in this patient is negative. It is not required in this case to diagnose early lyme disease given that she has strong clinical features to support the diagnosis.


  8. I agree tetracycline for non prego &Ampicillin for prego
    this is the bull’s eye rash

  9. Erythema chronicum migrans refers to the rash often (though not always) seen in the early stage of Lyme disease. It can appear anywhere from one day to one month after a tick bite. This rash does not represent an allergic reaction to the bite, but rather an actual skin infection with the Lyme bacteria, Borrelia burgdorferi sensu lato. “Erythema migrans is the only manifestation of Lyme disease in the United States that is sufficiently distinctive to allow clinical diagnosis in the absence of laboratory confirmation.”. It is a pathognomonic sign: a physician-identified rash warrants an instant diagnosis of Lyme disease and immediate treatment without further testing, even by the strict criteria of the Centers for Disease Control. These rashes are characteristic of Borrelia infections and no other pathogens are known that cause this form of rash. ( WIKIPEDIA)

  10. It is really nice , tricky question to do mistake with timing and exam nervousness.

  11. B

  12. C

  13. B

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