WBR0060
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology, MainCategory::Pharmacology |
| Sub Category | SubCategory::Dermatology, SubCategory::General Principles, SubCategory::Infectious Disease |
| Prompt | [[Prompt:: A 34 year old woman presents to your office complaining of a rash which started on her palms and soles but has begun spreading to her wrists and ankles. She has been experiencing headaches, malaise and progressive fever. She does not drink or smoke, but is sexually active. She reports no international travel but recently returned from a vacation on Cape Cod. What is the proper treatment for the most likely causal organism?]] |
| Answer A | AnswerA::Doxycycline |
| Answer A Explanation | AnswerAExp::Correct - See Explanation |
| Answer B | AnswerB::Erythromycin |
| Answer B Explanation | AnswerBExp::Incorrect - Erythromycin is a macrolide antibiotic which blocks ribosomal translocation. It is used for atypical pneumonias such as mycoplasma infections. |
| Answer C | AnswerC::Ampicillin |
| Answer C Explanation | AnswerCExp::Incorrect - Ampicillin is an extended spectrum Beta-Lactamase which helps to kill enterococci. |
| Answer D | AnswerD::Trimethoprim-Sulfamethoxazole |
| Answer D Explanation | AnswerDExp::Incorrect - TMP-SMX (Bactrim) inhibits bacterial folate synthesis and is most commonly used for UTIs. |
| Answer E | AnswerE::Cephalexin |
| Answer E Explanation | AnswerEExp::Incorrect - Cephalexin is a first generation cephalosporin which is also a beta-lactam based drug and inhibits cell wall synthesis. It is most commonly used against gram positive cocci. |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The patient in this vignette has been infected with Rickettsia Ricketssii which causes Rock Mountain Spotted Fever. Patients with Rocky Mountain Spotted Fever are infected through Dermacentor tick bites and the Rickettsial organism is endemic to the East Coast despite its name. A hallmark of infection is a rash starting at the palms and soles which extends to the wrists and ankles over time. Very few organisms cause rash on the palms and soles, only Coxsackie A, Rickettsia Rickettssi and Syphilis (think CARS). Rocky Mountain Spotted Fever can be diagnosed by a Weil-Felix test in which patient serum is incubated with Proteus antigens and agglutination is considered a positive test. Finally, all Rickettsia are intracellular organisms which require CoA and NAD+, and all infections are treated with doxycycline, a tetracycline antibiotic which inhibits 30S ribosome binding to aminoacyl-tRNA.
Educational Objective: Rocky Mountain Spotted Fever is treated with doxycycline.
References: First Aid 2012 page 168
Tags: #Microbiology #Pharmacology |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |