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Retired NBME 24 Answers

nbme24/Block 4/Question#41 (reveal difficulty score)
A 30-year-old man who is a migrant farm ...
Formation of hypnozoites ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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 +16  upvote downvote
submitted by โˆ—jejunumjedi(30)
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The blood smear depicts Schuffner stippling. Found the exact image on the web with explanation:

http://spot.pcc.edu/~jvolpe/b/bi234/lec/2_parasites/images/P._vivax.htm

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doctorboomboom  Hey thanks for finding the image! Do you know why the answer canโ€™t be Chloroquine resistance? I was b/w that and formation of hypnozoites. +6
jejunumjedi  I think it's just that Schuffner stippling and hypnozoites are both specific to vivax and ovale species. These species could be chloroquine resistant or sensitive, but if you have Schuffner stippling or hypnozoites, you can definitively say that it's either vivax or ovale. +3
sherry  Species with hypnozoites is not called chloroquine resistant. Chloroquine-resistant species means trophozoite/schizont cant be killed by chloroquine. We dont have enough info to decide whether the spp in the q is resistant/sensitive. But we do know he moved from Honduras to USA 1 year ago. +3
soph  UW: in africa most malaria species are resistant to chloroquine. he is from hondruas +6
randios  Can anyone explain the 1-week history of fever? Ruled out vivax and ovale due to 48 hr cycles. Or did they just throw that in as an unspecific symptom. +2
dr_ligma  unspecific symptom probably +
mcm94  how I know that is an infection by vivax/ovale ? if there's nothing that says about tertian fever? +3
medguru2295  While it COULD be Chloroquine resistant, its not likely. This patient is likely infected with Vivax or ovale (not Falciparium) why? 1. Honduras (Falcip would be Africa) 2. Sx 1 year later (Liver form Vivax or OVale) 3. As many mentioned, Schuffer bodies Falciparium tends to be the species resistant to Chloroquine. Typically, Chloroquine is given for Vivax & Ovale (typically with something else- Atovaquone, Dapsone etc) to cover Liver Falciparium (no Liver form) is generally Chloroquine resistant (B) and therefore covered with Atovaquone/Proguanil. You do need 8-14 days of tx after coming for Falcip bc it can remain in the Liver for a few days (just not a dormant hypno form). To cover the "week of fever" question- its re-emergence of her sx. They probably just did not want to say cyclic to make it trickier. +6
flvent2120  Looks like it's been touched on, but you could answer this solely based on the fact that it's been one year since living in Honduras. While it MAY be chloroquine resistant, it IS dormant. Test taking skills would be to choose the answer you can't argue with +
meryen13  @doctorboomboom I think because its showing that its been a year since he immigrated ( late showing of the dz) its hinting toward the hypnotizes. not sure. +


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 +14  upvote downvote
submitted by โˆ—suckitnbme(239)
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Even if you can't interpret the blood smear, this patient is presenting with malaria after being in the US for 1-year. It's highly unlikely that he got newly infected while in the US. What is occurring is a reactivation of dormant malaria (hypnozoites in the liver) that this dude got while in Honduras.

As such this is plasmodium vivax/ovale. What probably happened was that this patient was treated with chloroquine when he was initially infected. This would clear the infection in the bloodstream, but does not kill the hypnozoites in the liver. Treatment with primaquine is needed to clear the hypnozoites, which this patient likely did not receive, hence malaria while in the US.

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madamestep  Yup! I got a similar question with no blood smear (Maybe on UWorld? They all blur together) and the clue was that they had malarial symptoms after being in America for a while. +


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 +7  upvote downvote
submitted by leny123(7)
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General rule - Chloroquine sensitive if from Caribbean or Central America west of Panama Canal, this patient immigrated from Honduras so you can eliminate chloroquine resistance as an answer choice (in addition to the vivax/ovale info above).

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charcot_bouchard  Guys along with all intelligent discussion also keep in mind he immigrated 1 year back. So it must be hypnozoites which is causing this because Murica is Malaria free. +28


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 +1  upvote downvote
submitted by โˆ—nwinkelmann(366)
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Found this great document with slides about the different pathogens: http://ncasmbranch.org/meetings/2019SprPpts/2019-03_Spring_Garcia.pdf

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 +1  upvote downvote
submitted by โˆ—yotsubato(1208)
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Kind of tricky question. The hypnozoites are chloroquine resistant. But the species may not be.

P. Falciparum is resistant and looks like a banana, but you dont know if the malaria in the RBC is falciparum or not.

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tyrionwill  whether resistant or sensitive, depends on the region, not on the species falci coming from Hatii could be sensitive +


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 +0  upvote downvote
submitted by โˆ—unknown001(9)
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RESOURCE : CDC Malaria species: P. vivax 93%, P. falciparum 7%.

WHY HYPNOZOYES ? 2 reasons

  1. schuffner stippling ( that wierd cell with lots of blue glitters)

  2. HONDURAS ( 93 percent are vivax)

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unknown001  https://wwwnc.cdc.gov/travel/destinations/traveler/none/honduras +


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 +0  upvote downvote
submitted by โˆ—paperbackwriter(161)
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Pg. 157 of 2019 FA picture B depicts Shuffner stippling under Malaria. "Seen with P vivax/ovale"

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 +0  upvote downvote
submitted by โˆ—krewfoo99(116)
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I think chloroquine resistance wont be specefic to vivax and ovale,thus making it the incorrect answer. Chloroquine resistance can apply to P. Falciparum and P. Malariae

Only vivax and ovale cause hypnozoite thus making that the more clear answer

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 +0  upvote downvote
submitted by โˆ—nwinkelmann(366)
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Does anyone know how to rule out E? I've never learned about microorganisms specifically activating a cell's CAMs, but when I looked it up, I found this article (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC395703/). The article doesn't specifically mention plasmodium as using it, but several of the resources for the article does.

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