WBR0297
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 40-year-old male presents to the emergency room with complaints of headache, fever, vomiting, and a rash, which began from his ankles and wrists and then proceeded to migrate towards the trunk. Physical examination reveals a fever of 38.89 °C, maculopapular rash ans swelling of the wrists and ankles. Which of the following organisms is most likely the cause of the patient's symptoms?]] |
| Answer A | [[AnswerA::Coxiella burnetti]] |
| Answer A Explanation | [[AnswerAExp::Coxiella burnetti often causes Q fever and does not manifest with a rash.]] |
| Answer B | [[AnswerB::Rickettsia typhi]] |
| Answer B Explanation | [[AnswerBExp::Rickettsia typhi often leads to endemic typhus, transmitted by fleas, and manifests with a rash that typically originates at the trunk.]] |
| Answer C | [[AnswerC::Rickettsia rickettsii]] |
| Answer C Explanation | AnswerCExp::See explanation |
| Answer D | [[AnswerD::Ehrlichia chaffeensis]] |
| Answer D Explanation | [[AnswerDExp::Ehrlichia chaffeensis, transmitted by ticks, does not manifest with a rash. It often leads to Ehrlichiosis and typically causes thrombocytopenia and leukopenia.]] |
| Answer E | [[AnswerE::Rickettsia prowazekii]] |
| Answer E Explanation | [[AnswerEExp::Rickettsia prowazekii ofetn causes epidemic typhus and manifests with a rash originating at the trunk.]] |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The patient in this scenario has Rocky Mountain spotted fever caused by Rickettsia rickettsii, an aerobic gram-negative bacillus. Rickettsia rickettsii, prevalent in the mountainous areas on the East Coast, has a 2-12 days incubation period. Rocky Mountain spotted fever manifests with a rash (maculopapular → petechiae), which originates at the ankles and wrists and then spreads to the trunk, palms, soles, and face (centripetal rash). Often, ankle and wrist swelling also occurs. The disease may be confused with gastrointestinal symptoms, periorbital swelling, stiff neck, conjunctivitis, and arthralgias.
Hard ticks, Dermacentors, with small wild rodents and larger wild and domestic animals being reservoirs, are often responsible for the transmission of Rocky Mountain spotted fever. Rickettsia rickettsii invades endothelial cells lining the capillaries, causing vasculitis in many organs, such as the brain, liver, skin, lungs, kidney, and gastrointestinal tract. Diagnosis is usually determined using a serological immunofluorescence antibody test and is also indicated by a 4-fold increase in titer. Although no longer commonly used, the Weil-Felix test would test positively in patients infected with Rickettsia rickettsii.
A palm and sole rash is also observed in Coxsackie virus A infection (hand, foot and mouth disease and Syphilis.
(MNEMONIC: CARS - Coxsackie virus A, Rocky Mountain spotted fever, Syphilis) |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Rash beginning from ankles and wrists |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |