USMLE NBME 18 - Questions and Answers - Discussions & Explanations

[TheAberrantGene]

NBME 18 has been released and is available on regular and extended feedback.
I will be taking it fairly soon as my exam is around the corner.
Let's continue the great trend on this forum and start a discussion once people start taking it,

Best of luck fellas !

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[Dr Tony T. Chopper]

okay I understand that 1st generation antihistamines have antimuscarinic effects but how does antagonism of M3 help with motion sickness. To the best of my knowledge, it does not. Antagonism of M1 could help with motion sickness but not M3. Can someone please help me out here? Why did NBME choose this as their answer???

Yeah I agree, this question is complete bull. M3 is only peripheral while M1 is the one that works in the brain. The part of Diphenhydramine that has anything to do with stopping motion sickness should be the portion that resembles Scopolamine, which works by blocking M1, NOT M3.....

 

[glandocephalon]

Hello guys, can someone provide a brief one sentence explanation (I really need explanation, not just correct answer) for these please. And THANK YOU in advance:

1. A 10 year old boy has nosebleeds and bruising. Three weeks ago had URI. PE shows ecchymosis. Hemoglobin and leukocyte count is normal but there is decreased platelet count. Bone marrow shows increased megakaryocytes. Which platelet abnormality is causing the findings?

A. Antibodies against glycoprotein IIb/IIIa
B. Decreased binding of Gp1a/IIa to collagen
C. Decreased concentration of Gp1B/IX
D. Decreased concentration of GpIIb/IIIa
E. Decreased synthesis of thromboxane A2
F. Deficient binding of vWf to Gp1b/IX


2. 25 year old woman with polycystic kidneys has fatigue, headaches, HTN, loss of appetite, itching. Creatinine is 4 mg/dL. State whether these are increased decreased or normal:

HCO3-
Inorganic PO4
PTH


3. Herniated lumbar intervertebral disc asking for most appropriate location for surgical entrance to neural canal?


4. 45 year old man comes to physician for follow up after appendectomy. There is mild scleral icterus and well healing surgical incision. Lab values show
Total bilirubin 3.2
Direct: 0.2
Indirect 3 mg/dL

What explains this?

A. Cholelithiasis
B. Gilbert
C. Hepatitis
D. Liver failure
E. Surgical bile duct trauma (wrong)

5. Man comes to doc for cast removal. Fracture of left humerus that required open reduction, internal fixation, cast immobilization. Muscle strength is 2/5 with extension of elbow and 1/5 with extension of wrist and fingers. Patient most likely sustained a fracture at (which location in humerus)?

A. Coronoid fossa
B. Distal shaft (wrong)
C. Medial epicondyle
D. Radial groove
E. Surgical neck

6. Question with Aortic aneurysm- it had history of smoking and HTN, and I know it said visible pulsation but also said murmur in second right intercostal space. So I chose Aortic Stenosis. How does this question make sense? Why can it NOT be aortic stenosis?

7. Old woman with bruising on forearms, wrinking, erythematous patches on face, brown macules. Echhymoses in various stages of healing. CBC and coagulation studies normal. What is causing ecchymoses:

A. Exocytosis of lymphocytes
B. Extensive solar elastosis (what is this??)
C. Impaired platelet function
D. UV destruction by Langerhans in epidermis

8. Woman with Pagets has right knee showing fracture of tibia and elevated periosteum and sunburst pattern (So Giant cell tumor?) Xray shows pul nodules of various sizes. What is the most likely finding on biopsy of tibia?

A. Closely packed, small, round, uniform neoplastic cels
B. Clusters of mucin-producing neoplastic cells forming glands
C. Neoplastic chondrocytes filing lacunes
D. Neoplastic plasma cells in sheets
E. Pleomorphic neoplastic cells producing new woven bone (why is this right?)

9. Woman with PID has surgical resection of scarred segment. What is going to be found in resected specimen?

A. Basophils
B. Eosinophils
C. Macrophages (dont tell me its this....whyy though?)
D. Mast cells
E. Neutrophils

10. Woman comes because of numbness, blanching, bluish color to ears, following emotional upset or exposure to cold. Avoid which drug?

A. Acetaminophen
B. Dextromethorphan
C. Diphenhydramine
D. Ibuprofen
E. Phenylephrine

THANKS a lot!!!

8. elevated periosteum and sunburst appearance=osteosarcome

 

[glandocephalon]

Nope, no1 answered me. I believe I chose beta1 on the exam and got it wrong tho

At a higher dose , dopamine acts on alpha-1 receptors.Hence, it is used in shock refractory to nor-epinephrine therapy.

 

[confused_and_tired]

18. A 4 year old boy has had a clumsy gait for the past year. Examination shows calf hypertrophy and proximal muscle weakness. Serum creatine kinase is ↑. Muscle biopsy shows loss muscle tissue, regenerating muscle fibers, and fibrosis. A maternal uncle had similar findings and died at age 15. The patient's 20 year old sister is pregnant; ultrasonography identifies a male fetus. Which of the following is the probability that this male fetus has inherited this disorder?
A) 0
B) 1/8
C)1/4
D) 1/2
E)3/4

I got this one wrong as well but I think 1/4 makes sense because it is the possibility that the woman is a carrier which would be be 1/2 and the chance that a male fetus would get the disease which is 1/2 so multiply is 1/4. I remember something like this on UWorld and the explanation was something akin* to that.

*FANCY WORDS that may not be used appropriately.

 

[confused_and_tired]

Q. 58-year-old man comes to the physician because of a 4-year history of recurrent cough productive of increased sputum. Use of over-the-counter cough suppressants has not resolved his symptoms. He has smoked 2 packs of cigarettes daily for 35 years. He has no family history of lung disease. His temperature is 37°C (98.6°F), pulse is 72/min, and respirations are 18/min. Physical examination shows cyanosis. Diffuse wheezing is heard on auscultation. Which of the following pulmonary cell types is most likely to be abnormal in this patient?

- Answer: Pseudostratified columnar epithelial cells (Other options: Alveolar Endothelial cells, Alveolar Macrophages, Type I or Type II pneumocytes)

I get that this is more likely Chronic Bronchitis with metaplasia of the pseudostratified columnar epithelium to stratified squamous, but would i be wrong in thinking of this as also having a component of centrilobular emphysema with alveolar endothelial cell damage ("abnormality")?

The question stem mentions his chief complaint as the increased sputum which would explained by the metaplasia. I had a similar thought process as you did, but then I saw the question stem and realized the better answer for the sputum is the metaplasia.

 

[confused_and_tired]

A 20-year-old woman at 27 weeks' gestation is admitted to the hospital because of a 12-hour history of intense uterine contractions occurring every 8 minutes. Her membranes ruptured 32 hours ago. Her temperature is 39.1°C(102.4°F), and pulse is 115/min. Physical examination shows tenderness of the uterus. Pelvic examination shows a closed cervix that is not effaced. The fetal heart rate is 210/min. Which of the following is the primary stimulus for her uterine muscle contractions?
A
) Decreased myometrial intracellular calcium
B
) Direct response to maternal hyperthermia
C
) Inflamed maternal decidua release of prostaglandin
D
) Maternal adrenocorticosteroid release
E
) Stressed fetal production and release of oxytocin

Okay, I put E as well and I read through the question about 6 times now and I just realized why E is incorrect. E implies that the stressed fetus is producing and releasing the oxytocin which is not true as the fetus does not make oxytocin, it's produced in the hypothalamus (and released via the posterior pituitary). Therefore, C is better as inflammation --> PGs --> contraction. Basically, this was a grammar question more than a physio question.... Thanks NMBE.

 

[txmed73]

Answer is hypertension. Hypertension increases the pressure within the ventricle, and this pressure overload eventually results in diastolic heart failure, which is associated with concentric enlargement. Myocardial cells hypertrophy and develop "boxcar nuclei" when having to generate increased pressure due to hypertension.

Dilated cardiomyopathy is associated with eccentric hypertrophy. Hypertrophic obstructive cardiomyopathy is associated with concentric hypertrophy.

 

[Olivia Benson]

NBME18 was harder than 17, no doubt. But I feel, my score drop had something to do with the fact that I was very nervous taking it since it had just come out a few days ago. I got some very silly ones wrong. I plan to do FA and Uworld system wise in the last days and I am saving form 16 for the end. I really want to break 250 :/. @vulnificus

What did you guys end up getting if you don't mind me asking?

 

[jqueb29]

Dilated cardiomyopathy is associated with eccentric hypertrophy. Hypertrophic obstructive cardiomyopathy is associated with concentric hypertrophy.

Not quite, as evidenced by the fact that the poster said they answered HOCM and got the question wrong. Dilated cardiomyopathy is indeed associated with eccentric hypertrophy. Concentric hypertrophy most commonly occurs from hypertension or aortic stenosis (anything that chronically increases the pressure the ventricle has to work against). While HOCM can be considered to fall within concentric hypertrophy, it's not a fully accurate description. HOCM is always associated with preferential thickening of the interventricular septum, and the absence of this indicates the cause of the concentric hypertrophy is definitely not HOCM.

 

[Princess135]

34 year old man with progressive rash on his feet. HIV antibody test is positive. What do you give him in addition to HAART?
Antibacterial
Antineoplastic

I thought antibacterial since it could be bacillary angiomatosis. Why is it antineoplastic? I guess they were going for kaposi sarcoma here, but how were we supposed to know which one without biopsy? Also, sketchymicro and wiki say that treatment of kaposi is HAART. why would you give an antineoplastic?


thanks in advance for all of the help!!

Actually the question showed an image which was significant for kaposi sarcoma and its associated with HIV/AIDS