WBR0434
| Author | [[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Neurology |
| Prompt | [[Prompt::A 28-year-old HIV-positive female presents to the emergency room with a high grade fever, headache, weakness, and tonic-clonic seizures. The patient has a recent history of anorexia. Laboratory work-up reveals CD4 count = 80 cells/µL per year. Head computer tomography (CT) scan demostrates multiple ring enhancing lesions in the frontal lobes. The patient requires treatment with a medication that uses which of the following mechanisms of action?]] |
| Answer A | AnswerA::Inhibition of heme polymerase activity |
| Answer A Explanation | [[AnswerAExp::Chloroquine, an antimalarial drug, is a plasmodium heme polymerase inhibitor.]] |
| Answer B | AnswerB::Inhibition of dihydrofolate reductase activity |
| Answer B Explanation | [[AnswerBExp::Pyrimethamine, a drug frequently used to treat toxoplasmosis, is a dihydrofolate reductase inhibitor.]] |
| Answer C | AnswerC::Free radical toxicity of organism’s DNA |
| Answer C Explanation | [[AnswerCExp::Metronidazole, an antibiotic and antiprotozoal, forms free radical metabolites that are toxic to bacterial DNA.]] |
| Answer D | AnswerD::Blockade of peptide bond formation at 50S ribosomal subunit |
| Answer D Explanation | [[AnswerDExp::Several antibiotics, including chloramphenicol, macrolides, clindamycin, streptogramins, and linezolid, block peptide bond formation at the 50S ribosomal subunit.]] |
| Answer E | AnswerE::Inhibition of DNA polymerase activity |
| Answer E Explanation | [[AnswerEExp::Antiviral medications, such as acyclovir, ganciclovir, foscarnet, and cidofovir are DNA polymerase inhibitors.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::Cerebral toxoplasmosis, caused by Toxoplasma gondii, is an opportunistic parasitic infection that frequently infects HIV-positive patients with CD4 counts < 100 cells/µL per year. Toxoplasmosis manifest with fever, headache, and new-onset seizures. Multiple ring-enhancing lesions upon cranial CT scan are characteristic. Treatment of cerebral toxoplasmosis includes pyrimethamine, a dihydrofolate reductase inhibitor, and sulfadiazine, a sulfa drug that is a dihydropteroate synthetase inhibitor. Educational Objective: Cerebral toxoplasmosis, frequently occurring in HIV-positive individuals with CD4 count < 100 cells/µL per year, often manifests with a fever, headache, and new-onset seizures.
Treatment of cerebral toxoplasmosis includes pyrimethamine, a dihydrofolate reductase inhibitor, and sulfadiazine, a sulfa drug that is a dihydropteroate synthetase inhibitor. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Toxoplasma gondii, WBRKeyword::toxomplasmosis, WBRKeyword::HIV, WBRKeyword::seizure, WBRKeyword::ring enhancing lesion, WBRKeyword::pyrimethamine, WBRKeyword::dihydrofolate reductase inhibitor |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |