WBR0235

Author	[[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology, MainCategory::Pharmacology
Sub Category	SubCategory::Neurology, SubCategory::General Principles
Prompt	[[Prompt::A 19-year-old boy is brought to his pediatrician’s office by his father. Over the past several days, the patient has been increasingly fatigued and has noticed that the left side of his face has become less expressive. He denies any sick contacts or recent changes in mood, appetite, or weight. The patient also denies recent travel, except for a camping trip with the local boy scouts approximately 2 months ago. He is sexually active with one partner and uses condoms regularly. Neurological exam is significant only for unilateral weakness of the facial muscles on the left side. The physician then performs further work-up and prescribes a pharmacologic agent to treat the patient's condition. What is the mechanism of action of the prescribed pharmacologic agent?]]
Answer A	AnswerA::Activator of tissue plasminogen
Answer A Explanation	[[AnswerAExp::TpA may be indicated for specific cases of ischemic stroke or myocardial infarction (MI). While a stroke may produce unilateral neurologic symptoms, stroke is far less likely than Lyme disease in a young patient who has recently returned from a camping trip.]]
Answer B	AnswerB::Nucleotide analogue
Answer B Explanation	AnswerBExp::Acyclovir is a nucleotide analogue that inhibits HSV replication. HSV can cause facial palsy, but it is a less common cause of facial palsy than Lyme disease, especially in a patient who has recently returned from a camping trip.
Answer C	AnswerC::Activator of antithrombin III
Answer C Explanation	AnswerCExp::Heparin activates antithrombin III. Heparin is indicated for thromboembolic diseases, which are less likely than Lyme disease in a young patient who has recently returned from a camping trip.
Answer D	AnswerD::Inhibitor of topoisomerase
Answer D Explanation	AnswerDExp::Fluoroquinolones are antibiotics that act by inhibiting topoisomerase activity. However, fluoroquinolones are not the optimal pharmacologic therapy to treat Lyme disease.
Answer E	AnswerE::Inhibitor of aminoacyl tRNA entry into ribosome
Answer E Explanation	AnswerEExp::Tetracyclines are antibiotics that act by inhibiting aminoacyl tRNA entry into ribosome. Tetracyclines are the optimal pharmacologic therapy to treat Lyme disease in adult patients.
Right Answer	RightAnswer::E
Explanation	[[Explanation::yme disease is a multi-organ disease that involves the skin, nervous system, the heart, and the musculoskeletal system. It is an infectious disease caused by the spirochete Borrelia burgdorferi, which is transmitted to humans by Ixodes tick bite. Characteristically, tick bites are non-painful, and ticks may persist on human skin for several days. For transmission of the infection to occur, the tick needs to bite the skin for at least one day. Lyme disease is a common infection in Europe and Northeast USA during the summer and spring. The diagnosis of Lyme disease is made clinically when patients report exposure to ticks and present with typical erythema migrans on physical examination. In contrast, disseminated disease is more difficult to diagnose, and serological testing is necessary with a two-step approach: First, a high-sensitivity ELISA Lyme disease may be classified clinically into 2 stages: Early Lyme disease: Characterized by erythema migrans (bull's eye lesion), which is the pathognomonic skin lesion of Lyme disease. Onset is usually between 3 and 30 days following tick bite. The most common location of erythema migrans is the lower extremities and the trunk. Patients with typical erythema migrans are generally administered empirical doxycycline with no need for further diagnostic work-up. Secondary Lyme disease: Characterized by the presence of neurological, cardiac, and rheumatic manifestations. Neurological signs may be variable and may present anytime from a few months to years following initial infection. Neurological manifestations include meningitis, encephalitis, radicular pains, flaccid palsy, and sensory abnormalities. In contrast, cardiac manifestation often appear after several weeks of initial infection. Manifestations include atrioventricular blocks, pericarditis, and rarely, pancarditis. Finally, musculoskeletal disease may develop several weeks to years after infection, and manifestations include bone and joint pain with possible edema and effusions of the large joints. Tertiary (chronic) Lyme disease: Characterized by chronic symptoms that may be present even when the organism is cleared. Manifestations may include persistent join pain and edema, chronic progressive encephalomyelitis, memory impairment, and chronic peripheral neuropathy. 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: Tetracyclines are antibiotics that act by inhibiting aminoacyl tRNA entry into ribosome. Tetracyclines are the optimal pharmacologic therapy to treat Lyme disease in adult patients. 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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