WBR0235

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category	SubCategory::Neurology, SubCategory::General Principles
Prompt	[[Prompt::A 16 year old boy is brought to his pediatrician’s office by his father. Over the past several days she has noticed that the left side of his face has become less expressive. He reports some fatigue. He denies any sick contacts, recent changes in mood or appetite. He denies any recent travel, except for a camping trip with the local boy scouts approximately 2 months ago. He is sexually active with one partner. His cardiovascular and respiratory exam is normal. His neurological exam is significant only for unilateral weakness of the facial muscles on the left side. What is the mechanism of action of the most appropriate pharmacotherapy for this patient?]]
Answer A	AnswerA::Activates tissue plasminogen
Answer A Explanation	[[AnswerAExp::This is the mechanism of TpA, which can be used to treat stroke or myocardial infarction. While a stroke may produce unilateral neurologic symptoms, stroke is far less likely than lyme disease in a young patient who has recently gone on a camping trip.]]
Answer B	AnswerB::Nucleotide analogue
Answer B Explanation	[[AnswerBExp::This is the mechanism of acyclovir, which is used to inhibit HSV replication. HSV can cause Bell’s palsy, but it is a less common cause of Bell’s palsy than Lyme disease and suspicion for Lyme disease should be elevated by the patient’s recent camping trip.]]
Answer C	AnswerC::Activates antithrombin III
Answer C Explanation	AnswerCExp::This is the mechanism of heparin. Heparin can be used for stoke, but stroke is far less likely than lyme disease in a young patient who has recently gone on a camping trip.
Answer D	AnswerD::Inhibits topoisomerase
Answer D Explanation	AnswerDExp::This is the mechanism of fluoroquinolones, which are not the treatment of choice for Lyme disease.
Answer E	AnswerE::Inhibits aminoacyl tRNA entry into ribosome
Answer E Explanation	AnswerEExp::This is the mechanism of tetracycline antibiotics which are the most appropriate pharmacotherapy for Borrelia Burgdorferi infection.
Right Answer	RightAnswer::E
Explanation	[[Explanation::The patient in this vignette is suffering from the disseminated stage of Lyme Disease. Lyme disease is caused by the organism Borrelia Burgdorferi, a bacteria which is carried by the Ixodes tick. In its early stages, Lyme disease causes a characteristic “bullseye” rash called erythema chronicum migrans in 80% of patients. Most patients exhibit flu-like symptoms in the early stages of infection. The incubation period of Lyme disease can vary greatly, but is typically 1 to 2 weeks. If untreated, Lyme disease can cause facial palsy and AV nodal block (secondary Lyme disease) progressing to chronic monoarthritis or migratory polyarthritis (tertiary Lyme disease). Lyme disease is treated with tetracycline antibiotics (eg doxycyline). Tetracyclines work by blocking entry of aminoacyl tRNAs into the bacterial ribosome, thereby inhibiting protein synthesis. Educational Objective: Lyme disease istreated with tetracycline antibiotics, which function by blocking entry of aminoacyl tRNAs into the bacterial ribosome, thereby inhibiting protein synthesis. References: First Aid 2014 page 141]]
Approved	Approved::Yes
Keyword	WBRKeyword::Lyme disease, WBRKeyword::Lyme, WBRKeyword::Borrelia Burgdorferi, WBRKeyword::Microbiology, WBRKeyword::Gram negative, WBRKeyword::Gram-negative, WBRKeyword::Bacteria, WBRKeyword::Zoonotic, WBRKeyword::Antibiotic, WBRKeyword::Antibiotics
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