WBR0189
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1] (Reviewed by Will Gibson)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 45-year old HIV positive woman presents to the emergency department with complaints of headache, cough, shortness of breath and blurred vision. Physical examination reveals lymphadenopathy, tachypnea, rales and papilledema. A CT scan of the head is normal but CSF examination reveals encapsulated organisms that stain with India ink. Which of the following correctly describes the causative agent?]] |
| Answer A | AnswerA::Dimorphic encapsulated yeast |
| Answer A Explanation | AnswerAExp::The only encapsulated fungal pathogen is Cryptococcus neoformans and it is monomorphic, not dimorphic. |
| Answer B | AnswerB::Monomorphic encapsulated yeast |
| Answer B Explanation | AnswerBExp::Monomorphic encapsulated yeast describes Cryptococcus neoformans, which is the causative agent in this vignette. |
| Answer C | AnswerC::Yeast with broad based budding |
| Answer C Explanation | [[AnswerCExp::Broad based budding yeast describes Blastomyces dermatitidis. Blastomyces is the rarest of the systemic mycoses and casuses chronic inflammatory lung disease. It is endemic to the Mississippi river valley, but is not a common cause of meningitis in HIV-positive patients.]] |
| Answer D | AnswerD::Consists of branching septate hyphae |
| Answer D Explanation | AnswerDExp::Aspergillus fumigatus consists of branching septate hyphae. Aspergillus is not a common cause of meningitis in HIV-positive patients. |
| Answer E | AnswerE::Spaghetti and meatballs appearance on KOH stain |
| Answer E Explanation | [[AnswerEExp::Spaghetti and meatballs on KOH stain describes Malassezia furfur, the causative agent of tinea versicolor.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The patient in this vignette has Cryptococcal meningitis, caused by Cryptococcus neoformans. HIV-positive individuals are at high risk of infection with Cryptococcus neoformans. The yeast are often found in the soil and in pigeon droppings. Spores can be inhaled and can disseminate hematogenously, causing systemic infection and meningitis in immunocompromised individuals.
There are several methods to diagnose cryptococcal meningitis. The first, is to examine the CSF microscopically for encapsulated yeast. This assay can be supplemented with an India Ink stain, as the capsule of the yeast will stain positively with the dye. The second method of rapid diagnosis is with a latex agglutination test. In this test, latex beads are coated with antibodies against the Cryptococcal capsular antigen. If the antigen is present in a CSF sample that is mixed with the beads, the beads will agglutinate. The organism can be cultured in Sabourad's agar. However, treatment is often initiated before culture results are conclusive. Patients with confirmed cryptococcal meningitis should be treated with Amphotericin B. Speed B, Dunt D. Clinical and host differences between infections with the two varieties of Cryptococcus neoformans. Clin Infect Dis. 1995;21(1):28-34. First Aid 2014 page 148]] |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Cryptococcus, WBRKeyword::Cryptococcus neoformans, WBRKeyword::HIV, WBRKeyword::Opportunistic infection, WBRKeyword::Fungus, WBRKeyword::Yeast |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |