Step I Parvovirus B19

[IDoIt4Love]

Advertisement - Members don't see this ad

I came across a question about the effects of Parvo B19 on a fetus. FA says it causes RBC destruction, leading to hydrops fetalis. However, the answer choices included both "hemolytic anemia" AND "non-immune hydrops." Seeing as how Parvo is both a cause of non-immune hydrops AND destroys RBCs, how can you say which answer choice is definitively the better answer?

 

[MrBeauregard]

It's tough to say without seeing the whole question. Obviously there was a detail in the question stem that they wanted you to notice that would enable you to make a distinction between one or the other.

 

[AndyRSC]

Incidentally, I was just watching some obstetrics videos. In one of them, the lecturer mentioned that B19 infects the RBC precursors in the marrow, preventing normal hematopoiesis, thereby causing severe anemia and high-output cardiac failure.

I would select "non-immune hydrops."

 

[IDoIt4Love]

Yes, the answer is non-immune hydrops, and I did pick that choice. And no, there were absolutely no other pertinent details in the question. The question says that a kindergarten teacher came to the doctor, worried that she may contract something from a child in her class who has a bright red rash that started on her cheeks and progressed down her shoulders and chest, eventually becoming lace-like in pattern. The question asks which of the following potential complications could result in the fetus if the mother contracted this disease, and the options included non-immune hydrops, hemolytic anemia, and 2 other totally unrelated complications.

 

[deleted103644]

I came across a question about the effects of Parvo B19 on a fetus. FA says it causes RBC destruction, leading to hydrops fetalis. However, the answer choices included both "hemolytic anemia" AND "non-immune hydrops." Seeing as how Parvo is both a cause of non-immune hydrops AND destroys RBCs, how can you say which answer choice is definitively the better answer?

Parvovirus B19 causes anemia, but not hemolytic.

It inhibits new RBC creation (reticulocyte count will be low/zero).

 

[IDoIt4Love]

Parvovirus B19 causes anemia, but not hemolytic.

It inhibits new RBC creation (reticulocyte count will be low/zero).

I thought it caused both aplastic crises and destruction of RBCs. Further, in FA (2012 ed., page 183) it says the aplastic crises are characteristic of the adult infection, whereas destruction of RBCs occurs in fetuses, leading to hydrops fetalis.

Is FA just wrong here?

 

[MrBeauregard]

I thought it caused both aplastic crises and destruction of RBCs. Further, in FA (2012 ed., page 183) it says the aplastic crises are characteristic of the adult infection, whereas destruction of RBCs occurs in fetuses, leading to hydrops fetalis.

Is FA just wrong here?

I've never seen that it causes destruction of RBCs. In patients with preexisting hemolytic anemias, the decrease in RBC production (through the aforementioned infection of red cell progenitors) coupled with the already decreased RBC lifespan results in aplastic crisis.

 

[lemonade90]

It definitely causes aplastic anemia. Perhaps any hemolysis it causes is secondary to another genetic diseases (e.g. exacerabation of an existing problem of G6PD due to increased oxidant stresses from the infection).

 

[Dr McSexy]

I've never seen that it causes destruction of RBCs. In patients with preexisting hemolytic anemias, the decrease in RBC production (through the aforementioned infection of red cell progenitors) coupled with the already decreased RBC lifespan results in aplastic crisis.

This is correct.

I'm pretty sure that FA is just wrong.

 

[CrimsonMirage]

After some web-searching articles, I found this: "parvovirusB19 may have an affinity for erythroid lineage cells at the hepatic stage of hematopoiesis, which may strongly influence the clinical features of feto-maternal B19 infection."

So by "RBC destruction" maybe FA was trying to say "destruction of RBC lineage in utero"? I definitely don't think Parvo B19 causes hemolytic anemia, b/c that would require formation and subsequent destruction of RBCs.

Immune hydrops fetalis --> erythroblastosis fetalis from Rh factor reaction
Non-immune hydrops fetalis --> wipeout of RBC lineage from Parvo B19

 

[deleted103644]

After some web-searching articles, I found this: "parvovirusB19 may have an affinity for erythroid lineage cells at the hepatic stage of hematopoiesis, which may strongly influence the clinical features of feto-maternal B19 infection."

So by "RBC destruction" maybe FA was trying to say "destruction of RBC lineage in utero"? I definitely don't think Parvo B19 causes hemolytic anemia, b/c that would require formation and subsequent destruction of RBCs.

Immune hydrops fetalis --> erythroblastosis fetalis from Rh factor reaction
Non-immune hydrops fetalis --> wipeout of RBC lineage from Parvo B19

That's still not hemolysis, it's inhibition of erythropoiesis.

 

[IDoIt4Love]

I think First Aid is just wrong. Robbins makes no mention of RBC destruction due to Parvo B 19 infection. I already sent the FA people a message to propose that this was an error. Thanks guys!