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 -1  (nbme22#41)

Everywhere I found (UpToDate and several papers) said the smoking is the biggest risk factor for spontaneous pneumothorax, with body habitus and gender being a lesser risk. Am I just completely misunderstanding the question?

imresident2020  Yes smoking is a risk factor but not the best option among the choices given. Check FA, it says that it occurs more in tall thin young males. Smoking isn’t even mentioned. Tall & thin males are more at risk because they have more negative intrapleural pressure. Check Uworld for this.
drdoom  You have to think about this using the concept of CONDITIONAL PROBABILITY. Another way to ask this type of question is like this: “I show you a patient with spontaneous pneumothorax. Which other thing is most likely to be true about this patient?” Said a different way: Given a CONDITION [spontaneous pneumo], what other finding is most likely to be the case? Still other words: Given a pool of people with spontaneous pneumothorax, what other thing is most likely to be true about them? In other words, of all people who end up with spontaneous pneumo, the most common other thing about them is that they are MALE & THIN. If I gave you a bucket of spontaneous pneumo patients -- and you reached your hand in there and pulled one out -- what scenario would be more common: In your hand you have a smoker or in your hand you have a thin male? The latter.
cocoxaurus  Rupture of pulmonary blebs are a common cause of spontaneous pneumothorax in young adult males that are tall and thin. I know it's also associated with smoking, but gender and body habitus seemed like the more likely answer here since the patient is a young male.

 +4  (nbme22#25)

Not 100% sure on this one, but here’s how I approached it: histamine causes arterial dilation (=decreased arteriolar resistance), but all of that blood has to go somewhere since you now have more blood flowing through the arteries and that somewhere is the capillaries (increased capillary hydrostatic pressure). Histamine causes increased permeability of the post-capillary venules (one of Dr. Sattar’s favorite facts) so you’d have increased capillary filtration rate.


 +5  (nbme22#9)

Our little friend has a Parvovirus infection, which infects erythroid precursors, causing interruption of erythrocyte production. This is the same way it causes hydrops fetalis in unborn babies and aplastic anemia in sickle cell, etc.

gainsgutsglory  I get Parvo has tropism for RBC precursors, but wouldn’t it take 120 days to manifest?
keycompany  RBCs don’t just spill out of the bone marrow every 4 months on the dot. Erythropoesis is a constant process. If you get a parvo virus on “Day 1” then the RBCs that were synthesized 120 days before “Day 1” will need to be replaced. They can’t be because of parvovirus. This leads to symptomatic anemia within 5 days because the RBCs that were synthesized 125-120 days before the infection are not being replaced.
drdoom  @gainsgutsglory @keycompany It seems unlikely that “1 week” of illness can explain such a large drop in Hb. It seems more likely that parvo begins to destroy erythroid precursors LONG BEFORE it manifests clinically as “red cheeks, rash, fever,” etc. Might be overkill to do the math, but back-of-the-envelope: 7 days of 120 day lifespan -> represents ~6 percent of RBC mass. Seems unlikely that failure to replenish 6 percent of total RBC mass would result in the Hb drop observed.
yotsubato  He can drop from 11 to 10 hgb easily
ls3076  Apologies if this is completely left-field, but I didn't think this was Parvovirus. Parvo would affect face. Notably, patient has fever and THEN rash, which is more indicative of Roseola. Thoughts??
hyperfukus  @is2076 check my comment to @hello I thought the same thing for a sec too :)
hyperfukus  also i think you guys are thinking of hb in adults in this q it says hb is 10g/dL(N=11-15) so it's not relatively insanely low
angelaq11  @Is3076 I completely agree with @hyperfukus and I think that thinking of Roseola isn't crazy, but remember that usually with Roseola you get from 3-5 days of high fever, THEN fever is completely gone accompanied by a rash. This question says that the patient has a history of 4 days of rash and 7 days of fever, but never mentioned that the fever subsided before the appearance of the rash. And Roseola is not supposed to present with anemia.

 +0  (nbme22#23)

Tamoxifen has to be metabolized via first pass metabolism to an active metabolite (endoxifen). The patient has decreased concentrations of the metabolized product indicating that the patient’s pair of cytochrome P450 alleles aren’t metabolizing tamoxifen correctly. The question is asking what the chances are the sister has the same genotype, which would be 25% --> 1/2 * 1/2 = 1/4

medschul  How do we know the parents are not homozygous
yotsubato  Chances are they are not unless they had or are incestuous




Subcomments ...

submitted by gribear(0),

Can someone explain why when you transect the spinal cord superior to the level of sympathetic outflow -- and you get a systemic infection -- the response is alteration of the thermostatic set point?

its_raining_jimbos  So I chose that one because set point is controlled by the hypothalamus (PGE2 and IL-1 mediate fever in the hypothalamus) and the rest of the answer choices involved something below the level that has been transected. Not 100% sure if that’s accurate though. +1  
noselex  Agreed with @its_raining_jimbos -- Fever is mediated by altering set point in hypothalamus. All the other choices, as far as I can tell, involve sympathetic nerves and their effects at target organs. +  


submitted by moneysacs(0),

Histamine causes a decrease in hydrostatic pressure (get this, it’s a vasodilator) but then causes an increase in capillary hydrostatic pressure? (Okay, this is how it causes edema, I guess.) Does anyone get how this actually works?

its_raining_jimbos  Not 100% sure on this one, but here’s how I approached it: histamine causes arterial dilation (decreased arteriolar resistance), but all of that blood has to go somewhere since you now have more blood flowing through the arteries and that somewhere is the capillaries (increased capillary hydrostatic pressure). Histamine causes increased permeability of the post-capillary venules (one of Dr. Sattar’s favorite facts) so you’d have increased capillary filtration rate. +