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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=Infectious Disease
|SubCategory=Infectious Disease
|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 was normal but CSF obtained revealed encapsulated organisms stained with India ink. Which of the following is correct concerning the causative agent?
|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?
|Explanation=The patient in this vignette has [[Cryptococcosis]], caused by [[cryptococcus neoformans]]. Cryptococcus neoformans grows as a yeast (unicellular) and replicates by budding.  C. neoformans makes hyphae during mating, and eventually creates basidiospores at the end of the hyphae before producing spores. Under host-relevant conditions, including low glucose, serum, 5% carbon dioxide, and low iron, among others, the cells produce a characteristic polysaccharide capsule.  When grown as a yeast, C. neoformans has a prominent capsule composed mostly of polysaccharides. Microscopically, the India ink stain is used for easy visualization of the capsule in cerebral spinal fluid. The particles of ink pigment do not enter the capsule that surrounds the spherical yeast cell, resulting in a zone of clearance or "halo" around the cells. This allows for quick and easy identification of C. neoformans. Unusual morphological forms are rarely seen. Cryptococcal antigen from [[cerebrospinal fluid]] is thought to be the best test for diagnosis of cryptococcal meningitis in terms of sensitivity though it might be unreliable in HIV-positive patients.
|Explanation=The patient in this vignette has [[Cryptococcosis]], caused by [[cryptococcus neoformans]].  
 
The clues in this vignette are HIV, headache, blurred vision, encapsulated organism in [[CSF]] and the India ink stain. Also note that Cryptococcus neoformans is monomorphic.
The clues in this vignette are HIV, headache, blurred vision, encapsulated organism in [[CSF]] and the India ink stain. Also note that Cryptococcus neoformans is monomorphic.
|AnswerA=It is a dimorphic encapsulated yeast
|AnswerA=Dimorphic encapsulated yeast
|AnswerAExp=It is a dimorphic encapsulated yeast. This is a wrong option because crytococcus neoformans is the only encapsulated fungal pathogen and it is monomorphic.
|AnswerAExp=The only encapsulated fungal pathogen is Cryptococcus neoformans and it is monomorphic, not dimorphic.
|AnswerB=It is a monomorphic encapsulated yeast
|AnswerB=Monomorphic encapsulated yeast
|AnswerBExp=Monomorphic encapsulated yeast describes Cryptococcus neoformans and the only one that stains with India ink to produce the features seen in the vignette.
|AnswerBExp=Monomorphic encapsulated yeast describes Cryptococcus neoformans, which is the causative agent in this vignette.
|AnswerC=It is a broad based budding yeast
|AnswerC=Yeast with broad based budding
|AnswerCExp=Broad based budding yeast is seen in Blastomyces dermatitidis and it is not encapsulated and the India ink is not typically used for its staining.
|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.
|AnswerD=It consists of branching septate hyphae
|AnswerD=Consists of branching septate hyphae
|AnswerDExp=It consists of branching septate hyphae describes Aspergillus.
|AnswerDExp=Aspergillus fumigatus consists of branching septate hyphae. Aspergillus is not a common cause of meningitis in HIV-positive patients.
|AnswerE=It can also be seen as spaghetti and meatballs on KOH stain
|AnswerE=Spaghetti and meatballs appearance on KOH stain
|AnswerEExp=It can also be seen as spaghetti and meatballs on KOH stain describes Malassezia furfur.
|AnswerEExp=Spaghetti and meatballs on KOH stain describes Malassezia furfur, the causative agent of [[tinea versicolor]].
|EducationalObjectives=Cryptococcus neoformans is a monomorphic encapsulated yeast that commonly causes meningitis in HIV patients.
|EducationalObjectives=Cryptococcus neoformans is a monomorphic encapsulated yeast that commonly causes meningitis in HIV patients.
|References=First Aid 2014 page 148
|References=First Aid 2014 page 148

Revision as of 19:17, 1 November 2014
Author [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]]
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 Cryptococcosis, caused by cryptococcus neoformans.

The clues in this vignette are HIV, headache, blurred vision, encapsulated organism in CSF and the India ink stain. Also note that Cryptococcus neoformans is monomorphic.
Educational Objective: Cryptococcus neoformans is a monomorphic encapsulated yeast that commonly causes meningitis in HIV patients.
References: 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::
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