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NBME Explanations

NBME 18 Questions and Answers

Discussion in 'USMLE Step 1' started by orthopod, Mar 12, 2016.

  1. jalibean88

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    For Block 2 #4--36 year old woman with 2 week history of fatigue, gum bleeding, bone pain, pallor, hepatosplenomegaly (she has APML) t(15;17) translocation. I know ATRA is used to treat APML...but I don't understand what they mean here. When all trans retinoic acid is given, shouldn't it be suppressing the RARA/PML gene? I know that histone acetylase activates but I am confused about what is going on here with the pretranscriptional complex and all. Can someone help? Thank you!!
     
  2. orthopod

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    @jalibean88 this could be seen as quite a tough question with a lot going on. But really they're just trying to ask about the MOA of ATRA.

    ATRA causes dissociation of the histone deacetylase complex, allowing the promyelocytes to mature into granulocytes.

    Quick search, I found this:
    "It has been demonstrated that the receptor undergoes a configurational change upon retinoid binding, which allows the dissociation of a corepressor complex with histone deacetylase (HDAC) activity and the recruitment of a coactivator complex with histone acetylase activity."

    If you're still interested, here's the free article on PubMed
     
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  3. 2o17

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    Hi want to point out a correction -
    block 2 , part 1 , q13
    4-year-old boy with fatigue and irritability for 2 months. Family visited rural Louisiana 5 months ago and ran around barefoot. Conjunctivae are pale. Labs shows normal wbc with 15% eosinophils. Stool prep shows parasite egg (picture). Cause of fatigue?

    The answer is correct - Microcytic anemia
    but it is not caused by Strongyloides stercoralis , it is caused by Necator americanus/Ancylostoma duodenale ( sucks blood and passes eggs in stool ) while Strongyloides stercoralis (doesnt suck blood and passes larvae in stool).

    Both are similar ➔ infect through walking barefoot and can cause pneumonia and gastroenteritis
     
  4. drawesome

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    Hey can you please explain how we figure this NBME 18 question out:-
    25 yr old man,history of facial flushing,rapid heart rate each time he consumes a small amount of alcohol. He participates in a study of alcohol tolerance. Molecular analysis shows presence of lysine (K487-oriental variant) for glutamate (E487- native variant) substitution in aldehyde dehydrogenase. Kinetic ch of enzyme variants Enzyme Km(NAD+) - E487-37,K487-5600
    MicroM Kcat(min-1) E487-180,K487-9.5
    Based on these findings,most likely cause of man's condition?

    Please explain! Thankyouu
     
  5. drawesome

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    hey please reply, i have my exam v sooon!!
    Also, 17 yr old boy with FSH = 5;and and low testosterone = 8 (Normal being 10-35)
    height 10th percentile, weight 25th percentile
    What is this disease ????? and why do we expect gynaecomastia??? Please explain both my queries please, i have my exam really soon :/
     
  6. vendock

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    #26 vendock, Aug 17, 2016
    Last edited: Aug 17, 2016
    Block 1 #14

    Found the other options, but would it be M1/H1 instead of M3?

    A healthy 5 year old boy is brought to the physician by his parents for a well-child examination. He has a history of motion sickness.physical examination shows no abnormalities. The parents are planning a vacation to Australia, and they ask the physician if they should give their son diphenhydramine during the trip for his motion sickness. which of the following is the most likely mechanism of action of this medication for motion sickness?
    a. agnoist at alpha1-adrenoreceptors
    b. agonist at beta1-adrenoreceptors
    c. agonist at N-methyl-D-aspartate receptors
    d. antagonist at histamine-2 (H2) receptors
    e. antagonist at muscarinic-3 (M3) receptors
    f. antagonist at serotonin receptors
     
  7. Jackson Gina

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    This was an androgen insensitivity syndrome, because FSH was normal and testosterone was low, meaning the HPO axis was intact, I think it also mentioned in the question that menses never started, and it was a blind vagina, something that indicated that this wasn't a genotype of female. And because of that FSH, sertoli cell function, and MIH were all intact, so were LH and testosterone just the effect of testosterone/DHT wasn't being responded too. The other options that were given were excluded by process of elimination. This question you had to get what the diagnosis was in order to answer.

    And to the question about the boy using diphenhydramine- it is absolutely an antihistamine acting on the histamine 1 receptor. An H2 receptor is what ranitidine and cimetidine work on ( H2 is in the gut). Absolutely got this wrong because I went with the obvious histamine receptor, when the answer was E, because it antagonizes muscarinic receptors too.

    I am aware this may not help you now as so much time has passed, but hope it helps the next person.
     
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  8. Doaa Amir

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    hello.
    could someone please explain how to do the nutritional/ calories question? whats the math?
     
  9. Jackson Gina

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    39. To decrease risk for cv disease 24 yo man begins diet. 1.53 95 kg BMI 32, Intends to lose 16 kg by limiting caloric intake to 2000 cal. to maintain the recommended protein intake (56g day); a balanced decreased in carbs and fat is required (caloric radio of fat and carbs is 30:55). which best describes number of calories that should be provided by fat in this its diet each day?
    - 630

    I assume this was the question that you meant in the thread. Well if the total caloric intake of the day is 2000 calories and he takes in 56 g of protein, well start there: 1g protein= 4 calories, 1 g carb= 4 calories, 1g alcohol=7 calories and 1 g fat= 9 calories (Check the First Aid it is also briefly mentioned there). Now 56 g protein is 224 calories. Now you have 2000 calories (total) subtract 224 calories (protein)=1776 calories left (fat and carb calories). Alright now 55% is carb. 55% of 2000 calories is 1100. 1100(carb)+224 (protein)+ x (fat)=2000 calories. OR Fat= (1776 calories of fat and carb-1100 calories from carbs)=fat calories. Of your choices an answer in the 600 to 650 range was the right answer and the only one that fit. And its more important in this case to reverse the question (do the math backwards to make sure your ratios fit.) 630/2000=30% (specifically 31.5%)

    I hope this helps.
     
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  10. Doaa Amir

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    Wow. Thanks a lot!!
    hanks
     
  11. Doaa Amir

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    When are the rest of the explanations coming up?
     
  12. orthopod

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    @Doaa Amir it's been tough to post them myself, but feel free to post your questions (per our posting guidelines) and the TestPirates community will be happy to help out.
     
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  13. Doaa Amir

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    Hello. Can someone please explain these 2 questions?

    29. 45-year-old homeless man found unconscious. Breath smells of alcohol. Vitals stable. PE shows bronzed skin and spider angiomata on chest. Labs: hemoglobin 10, hematocrit 30%, MCV 110, WBC 9000, platelets 160,000, ferritin 200, b12 500, folate 20. Blood smear shows hypersegmented neutrophils and 3+ oval macrocytes. Labs?
    - Methylmalonic acid: normal, Homocysteine: increased


    45. 52 yo man is brought to er 30min after the onset of chest pain and shortness of breath. He had played tennis all day and he does not remember how much fluid he had consumed. His temperature is 36.7 oC, pulse 122min, respirations 28min and BP 90/50 mmHg. PE shows dry skin and decreased capillary refill. An ECG and evaluation of cardiac enzymes show no abnormalities. Which of the following findings in the nephron best describes the tubular osmolarity, compared with serum in this patient?
    PT //macula densa //medullary collection duct
    - Isotonic, hypotonic, hypertonic (?)

    thanks :)
     
  14. conan

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    The question is trying to trick you. Need to differenciate difference between B12, B6, or Folic acid deficiency. In biochemistry, Vitamin B12:

    Heme<----------B6----------Succinyl-CoA<-------B12---------Methylmalonyl-CoA

    Cysteine<-------B6----------Homocysteine------B12/THF-------->Methionine

    Since the vignette suggests Folate deficiency. Since THF is deficient. you will have a build up homocysteine because homocystine cannot be converet to methionine without B12 and Folate. However methylmalonyl-CoA conversion to Succinyl-CoA only need B12 which pt has plenty of. As a result Methylmalonic acid: normal, Homocysteine: increased.
     
  15. conan

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    Chillaxbro's answer on SDN: https://forums.studentdoctor.net/th...swers-discussions-explanations.1186685/page-7

    Picture is worth a thousand words.

    PCT is isotonic - correct

    Macula densa - reads the DCT, which is the most dilute - correct

    Medullary collecting duct - ADH absorbs all the water so hypertonic - correct

    [​IMG]
     
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  16. conan

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    My way was:

    total calories = protein + fat + carbs
    (carbs and protein = 4cal/g and fat= 10cal/g, you only need to know carbs is 4cal/g to solve this question)
    2000 = 56g (4 cal/g) + 30x + 55x
    solve for x:
    1776 = 85x
    x = 21
    so fat calories = 30 x 21 = 630
     
  17. orthopod

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    Thanks @conan, the picture definitely helps.
     
  18. Optimus

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    Hi, can you please explain this?

    #A 48 yrs old woman with gradual onset of back pain. No H/O trauma, tobacco, alcohol or illegal drug. Hemogram, serologic studies and urinalysis normal. Xray -spine shows 2 lyric lesion. What's the Dx?

    Key was Metastatic Ca of breast.
    But why not thyroid carcinoma ( coz breast n lung cancer - mixed ostroblastic & osteolytic lesion. In Thyroid cancer it's osteolytic only)

    ## 45 yrs old man with 6month H/O progressive shortness of breath with exertion. H/o frequent nosebleed. BMI 25kg/m2. Albuterol doesn't improve his S/S. 2 photograph- tongue bleeding point & clubbing.

    Key answer: Plumonary A/V shunting.

    Can u explain y? Whats the Dx?
    TIA
     
  19. orthopod

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    Thanks for the question!

    For your first question, the key here is remembering the phrase, "common things are common." Of course thyroid ca can cause lytic lesions in the spine; however, it is more common to see a 48yo F with a lytic lesion in her spine as a result of metastatic breast cancer rather than thyroid ca. Hope this makes sense.

    I can't comment on your second question with 100% certainty, so hopefully someone else can chime in here.

    Let us know if you have any other questions!
     
  20. SaharKh

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    The answer to your 2nd question is Hereditary Hemorrhagic Telangiectasia.
     

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