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Comments ...

 +5  (nbme24#50)

So the best i could find was in First Aid 2019 pg 346 under Diabetic Ketoacidosis. The hyperglycemia and hyperkalemia cause an osmotic diuresis so the entire body gets depleted of fluids. Hence why part of the treatment for DKA is IV fluids. You might even rely on that piece of information alone to answer this question, that DKA is treated with IV fluids.

fulminant_life  I just dont understand how that is the cause of his altered state of consciousness. Why wouldnt altered affinity of oxygen from HbA1c be correct? A1C has a higher affinity for oxygen so wouldnt that be a better reason for him being unconscious?
toupvote  HbA1c is more of a chronic process. It is a snapshot of three months. Also, people can have elevated A1c without much impact on their mental status. Other organs are affected sooner and to a greater degree than the brain. DKA is an acute issue.
snafull  Can somebody please explain why 'Inability of neurons to perform glycolysis' is wrong?
johnson  Probably because they're sustained on ketones.
doodimoodi  @snafull glucose is very high in the blood, why would neurons not be able to use it?
soph  @snafull maybe u are confusing bc DK tissues are unable to use the high glucose as it is unable to enter cells but I dont think thats the case in the neurons?

 +3  (nbme24#46)

I think more generally, protein folding happens at the RER and the stem says the protein doesn’t fold properly. Specifically, the most common CF mutation is a misfolded protein and the protein is retained in the RER and not transported to the cell membrane - FA 2019 pg 60.


 +3  (nbme23#26)

Page 592 on First Aid 2019 under Renovascular Disease. Main causes of renal artery stenosis: Fibromuscular dysplasia in the distal 2/3rd of renal artery or segmental branches, usually young or middle-aged females.


 +2  (nbme23#24)

This question is word for word in First Aid 2019 page 424 under CML. -- I did't realize it was there until I got it wrong.

vshummy  "Very low leukocyte alkaline phosphatase (LAP) as a result of low activity in malignant neutrophils vs benign neutrophilia (leukemoid reaction) in which LAP is increased due to increased leukocyte count with neutrophilia in response to stressors (eg, infections, medications, severe hemorrhage)."




Subcomments ...

submitted by colonelred_(44),

The diagnosis is strawberry hemangioma, commonly happens in kids, often resolves on its own as they get older.

shaeking  A strawberry hemangioma is normally pink or red (which is why it is named strawberry). The description has a flat purplish lesion which makes me think of a port wine stain on the face. How do you know to think of strawberry hemangioma over port wine based on this question stem? +  
sheesher  This sounds more like a nevus simplex, which is very similar to a port wine stain, though it regresses over time. +2  
seagull  the age is key here. Newborns have strawberry hemangiomas typically on their face. Sturge-Weber could also be the case but none of the answer choices matched to that description. +1  
vshummy  I would agree with Sturg Webber nevus flammeus but I also noticed First Aid says it's a non-neoplastic birth mark so I should have known not to pick malignant degeneration or local invasion. Also because capillary hemangiomas don't have to be flat but the nevus flammeus is consistently flat. But I'm also reading on Wiki that the nevus flammeus doesn't regress so they must be trying to describe strawberry hemangioma even though I don't agree with their color choice... +  
nala_ula  Maybe (and I can only hope I'm right and the test makers are not -that much of- sadists) they would have made sure to write "in a cranial nerve 5 (either ophthalmic or maxillary) distribution" if it were Sturge-Weber. +1  


submitted by karljeon(19),

I don't know if there is an equation for this, but I basically pumped out every division across the table to get ~5% on average.

Here they are: 400 / 6,000 = 0.067 250 / 5,600 = 0.045 300 / 5,350 = 0.056 300 / 5,050 = 0.059 250 / 4,800 = 0.052

The average of these %s for all the years = 5.58%. So that's close enough to 5%.

seagull  good work. I found this question annoying and gave up doing those considering the amount of time we are given. +1  
vshummy  Well just don’t include the intake year... because that messed me up.. +4  
_yeetmasterflex  How would we have known not to include the intake year? From average **annual** incidence? +  
lamhtu  Do not include intake year because the question stem is asking average annual incidence. The 4000 positives at intake could have acquired HIV whenever, not just in the last year. +1  
neels11  literally didn't think there was an actual way to figure this out. but my thought process was: okay incidence means NEW cases. so the annual average at the end of 5 years would be: (# of NEW people that tested positive at the end of year 5) / (# of people at that were at risk at the beginning of year 5) <--- aka at the end of year 4 250/5050 = 4.95% also if you look at year 5: you'll see that the at risk population is 4800 when 300 new cases were found the year before. 5050 at the end of year 4 MINUS the 300 new cases at the end of year 4 should give you 4750 as the new population at risk. but notice that end of year 5 we have 4800. idk if that means 50 people were false positives before or 50 people were added but in incidence births/death/etc don't matter it's kind of like UWORLD ID 1270. assuming average annual incidence is the same as cumulative incidence this was just a bunch of word vomit. sorry if it was unbearable to follow +  


submitted by lsmarshall(181),

Synaptobrevin is the target of tetanospasmin (tetanus toxin); muscle spasms are characteristic. Only other answer you might consider is Acetylcholinesterase since he is a farmer and buzzwords often carry us to the promised land... but symptoms of a cholinergic storm are absent.

vshummy  Synaptobrevin is a SNARE protein. Why they couldn’t just give us SNARE I’ll never know. +12  
yotsubato  Cause they're dicks, and they watched sketchy to make sure our buzzwords were removed from the exam +7  
yotsubato  Oh and they read FA and did UW to make sure its not in there either +6  
soph  This toxin binds to the presynaptic membrane of the neuromuscular junction and is internalized and transported retroaxonally to the spinal cord. Enzymatically, tetanus toxin is a zinc metalloprotease that cleaves the protein synaptobrevin, an integral neurovesicle protein involved in membrane fusion. Without membrane fusion, the release of inhibitory neurotransmitters glycine and GABA is blocked. -rx questions! +  


The disease here is fructose bisphosphatase deficiency. In it, IV glycerol or fructose doesn’t help because both enter the gluconeogenesis pathway below fructose bisphophatase. Galactose on the other hand enters above it. I don’t think you really need to know this to choose the correct answer since the clinical picture of fasting hypoglycemia that is corrected w/ some sort of sugar that can enter the gluconeogenesis pathway should clue you into the right answer.

neonem  I don't think you could have *totally* ruled out the other answers - I picked glycogen breakdown because it sounded kind of like Von Gierke disease (glucose-6-phosphatase) to me: characterized by fasting hypoglycemia, lactic acidosis, and hepatomegaly since you're not able to get that final step of exporting glucose into the blood. However, I guess in this case you wouldn't see that problem of glycerol/fructose infusion not increasing blood glucose. Nice catch. +6  
vshummy  I think you were super smart to catch Von Gierke! Just to refine your answer b/c I had to look this up after reading your explanation, von gierke has a problem with gluconeogenesis as well as glycogenolysis. So they’d have a problem with glycerol and fructose but also galactose since they all feed into gluconeogenesis before glucose-6-phosphatase. Great thought process! +7  


submitted by m-ice(116),

Vincristine is a chemotherapeutic drug that stabilizes microtubules and prevents them from disassembling. The cell in the picture is stuck in anaphase, with microtubules attached to its chromosomes, unable to pull them apart because it cannot disassemble its microtubules.

vshummy  So I get that by process of elimination cyclophosphamide, cyclosporine, doxorubicin, and 5-fluorouracil are not related to microtubules but vincristine in First Aid 2019 says it prevents microtubule formation, doesn’t stabilize it because the one that stabilizes microtubules is paclitaxel. +  
vshummy  Okay, I realize now- the picture is stuck in metaphase, not anaphase. Both paclitaxel and vincristine stop the cell in metaphase but by two different mechanisms. Vincristine prevents mitotic *spindle* formation while paclitaxel prevents mitotic spindle *breakdown*. Mitotic spindle is needed to pull the chromosomes apart before anaphase begins. +5  


submitted by m-ice(116),

Vincristine is a chemotherapeutic drug that stabilizes microtubules and prevents them from disassembling. The cell in the picture is stuck in anaphase, with microtubules attached to its chromosomes, unable to pull them apart because it cannot disassemble its microtubules.

vshummy  So I get that by process of elimination cyclophosphamide, cyclosporine, doxorubicin, and 5-fluorouracil are not related to microtubules but vincristine in First Aid 2019 says it prevents microtubule formation, doesn’t stabilize it because the one that stabilizes microtubules is paclitaxel. +  
vshummy  Okay, I realize now- the picture is stuck in metaphase, not anaphase. Both paclitaxel and vincristine stop the cell in metaphase but by two different mechanisms. Vincristine prevents mitotic *spindle* formation while paclitaxel prevents mitotic spindle *breakdown*. Mitotic spindle is needed to pull the chromosomes apart before anaphase begins. +5  


Why would it not be anemia of chronic disease with decreased serum transferrin concentration?

lispectedwumbologist  Nevermind I'm stupid as fuck I see my mistake +  
drdoom  be kind to yourself, doc! (it's a long road we're on!) +7  
step1forthewin  Hi, can someone explain the blood smear? isn't it supposed to show hypersegmented neutrophils if it was B12 deficiency? +  
loftybirdman  I think the blood smear is showing a lone lymphocyte, which should be the same size as a normal RBC. You can see the RBCs in this smear are bigger than that ->macrocytic ->B12 deficiency +8  
seagull  maybe i'm new to the game. but isn't the answer folate deficiency and not B12? Also, i though it was anemia of chronic disease as well. +  
vshummy  Lispectedwumbologist, please explain your mistake? Lol because that seems like a respectible answer to me... +  
gonyyong  It's a B12 deficiency Ileum is where B12 is reabsorbed, folate is jejunum The blood smear is showing enlarged RBCs Methionine synthase does this conversion, using cofactor B12 +  
uslme123  Anemia of chronic disease is a microcytic anemia -- I believe this is why they put a lymphocyte on the side -- so we could see that it was a macrocytic anemia. +  
yotsubato  Thanks NBME, that really helped me.... +  
keshvi  the question was relatively easy, but the picture was so misguiding i felt! i thought it looked like microcytic RBCs. I guess the key is, that they clearly mentioned distal ileum. and that is THE site for B12 absorption. +2  
sahusema  I didn't even register that was a lymphocyte. I thought I was seeing target cells so I was confused AF +  


submitted by vshummy(44),

This question is word for word in First Aid 2019 page 424 under CML. -- I did't realize it was there until I got it wrong.

vshummy  "Very low leukocyte alkaline phosphatase (LAP) as a result of low activity in malignant neutrophils vs benign neutrophilia (leukemoid reaction) in which LAP is increased due to increased leukocyte count with neutrophilia in response to stressors (eg, infections, medications, severe hemorrhage)." +  


submitted by docred123(3),

Can someone please further explain this question? What biostatistical analysis should I be thinking about?

vshummy  I got this wrong but best I could come up with was this was about Bradford Hill Criteria for establishing causality. And of the 9 included, F has the most that are actually included in the information given to us. I chose D but I think since we don't know about other study results, we can't include it as directly answering the question about *this* study. https://en.m.wikipedia.org/wiki/Bradford_Hill_criteria Someone double check me here: A: biologic plausibility is a weak point in the criteria, according to the wiki. Also probably not true in regards to this study. B: Sensitivity is not part of the criteria C: " " D: We don't know about consistency E: " B " +3  
mousie  Found this ... still confused about why A and D are wrong though... https://stats.stackexchange.com/questions/534/under-what-conditions-does-correlation-imply-causation +1  
2zanzibar  The three criteria for causality are: 1) empirical association (i.e. strength of association; a change in independent variable correlates or is associated with a change in dependent variable), 2) time order (i.e. temporal relationship; the independent variable must come before change in the dependent variable, or plainly stated, cause must come before effect). and 3) nonspuriousness (i.e. dose-response gradient; the relationship between 2 variables is due to a direct relationship between the two, not because of the actions of changes in a third variable... this can be evinced by a dose-dependent response). +5