| * NBME 13 answer key
Some questions are missing in the download for block 1 and 2. Block 2 q 23..not sure if its A, hence the (). Open for discussion people!
|* Re:NBME 13 answer key
1- (E) EBV infects B-lymphocytes, but the cells that react to the infection are T-lymphocytes because it is a viral infection. In EBV infection the reactive T cells undergo some morphologic changes (become enlarged with abundant vacuolated cytoplasm) and are called atypical lymphocytes.
2- (E) Erythromycin, like other macrolides, works by inhibiting translocation of the ribosome along the mRNA. Choice B is puromycin, C is diphtheria toxin, and D is tetracyclines.
3- (B) Hemangioma is a benign tumor that arises from the endothelial cells that line the blood vessels.
4- (E) Sumatriptan activates 5HT1B/1D receptors, which are serotonin receptors.
5- (C) Positive predictive value (PPV) equals (TP/TP+FP), when the prevalence increases, the rate of the false positive (FP) decreases and so the PPV increases.
6- (B) Hyperreflexia (sign of UMN lesion) + fasciculations (sign of LMN lesion) indicate most probably a case of amyotrophic lateral sclerosis (ALS). It is characterized by difficulty swallowing due to paralysis of the somatic muscles of the pharynx and upper esophagus.
7- (C) Staphylococcus aureus most probably caused the acute endocarditis in much the same way it causes it in IV drug abusers; by getting access from skin wound into the right side of the heart.
8- (J) Typical description of VSD.
9- (D) A case of ovarian torsion, which causes obstruction of the ovarian blood vessels that pass through the suspensory ligament of the ovary leading to ovarian ischemia.
10- (C) Most probably a case of Giardia lamblia, the diagnosis can be made by visualizing ova and parasites in the stool
11- (A) Bevacizumab is a humanized monoclonal antibody directed against VEGF, it comes from human origin using recombinant DNA technology, and thus it doesn’t encounter a strong immune response against them, unlike antibodies extracted from other species that encounter a strong immune response leading in many cases to type III hypersensitivity reactions (serum sickness)
12- (A) The patient most likely has a prolactin secreting pituitary adenoma, the treatment is with a dopamine agonist (like bromocriptine of cabergoline) that inhibits prolactin production and in the majority of patients leads to shrinkage of tumor size.
13- (C) The photograph shows the neuromuscular junction, Lambert-Eaton syndrome is an autoimmune disorder caused by production of Abs against the presynaptic calcium channels at the NMJ, leading to inhibition of Ach release; it usually involves the proximal muscles especially of the lower limbs, and is associated with cancer.
14- (C) HPV E6 protein is the only foreign protein shown, and thus it would produce the strongest immune response, all the other proteins are self-proteins.
15- (E) These symptoms are suggestive of carcinoid syndrome caused by metastatic carcinoid tumor; the most common primary site for this tumor is the appendix followed by the small intestine.
16- (A) The stem describes a branchial cyst, formed due to incomplete obliteration of the second branchial cleft by the branchial arch during embryonic development; it is found in front of the anterior border of the sternomastoid muscle. (N.B. The other cystic neck swelling, cystic hygroma, is found along the posterior border).
17- (C) The most plausible answer is inhibition of CYP450, but I can’t come up with a good explanation for it.
18- (C) Having an affected child with an AR disease means that both parents are carriers, so the probability the next child is 50% being carrier, 25% being homozygous normal, and 25% being affected with the 2 recessive alleles.
19- (D) The case describes mucopolysaccharidosis (specifically Hunter’s syndrome) that’s X-linked and is characterized by the deficiency of iduronate sulfatase enzyme that metabolizes mucopolysaccharides as heparan and dermatan sulfate.
20- (F) One of the most serious side effects of metformin is lactic acidosis, due to inhibition of aerobic metabolism in muscles.
21- (D) The case describes mitochondrial myopathy in which “ragged-red fibers” is a characteristic finding. The most important mitochondrial process that becomes impaired in these patients is oxidative phosphorylation, and this impairment is the cause of elevated lactic acid.
22- (E) The use of gentamicin (nephrotoxic drug), high urinary Na level (>20 mEq/L) and the presence of brown granular cast all suggest a case of ATN which mostly affects the PCT because it is the most metabolically active and energy demanding part of the kidney.
23- (A) Since the patient is borderline obese, the most important recommendation would be to lower his weight. A low calorie diet that takes into account all types of food taken is more efficient than targeting any single category.
24- (E) High carboxyhemoglobin indicates CO poisoning, CO impairs oxidative phosphorylation in the mitochondria by inhibiting the last step catalyzed by the enzyme cytochrome oxidase (aka Cyt a+a3)
25- (A) In cases of acute inflammation such as this one (acute appendicitis) certain cytokines released from the PMNs and macrophages in the inflammation site act on the hypothalamus to produce fever, the most important of these mediators are TNF, IL-1, IL-6.
26- (C) The question needs you to know the function of the protease enzyme. Other viral enzymes like reverse transcriptase, integrase, etc. first get formed as a part of big polypeptide chain that’s located in the core of the virus; the protease functions to break down that polypeptide to release those enzymes, thus leading to the maturation of the core.
27- (B) Struvite stones are formed in an alkaline medium, such a medium is promoted by a bacterium that has a urease enzyme which can break down the urea into ammonia and thus cause alkaline pH. The only bacterium listed that has urease enzyme is proteus.
28- (B) A patient complaining to you about his physician--> encourage the patient to communicate with the physician.
29- (B) Sensory deficit in the left hand--> a problem in the right somatosensory cortex located in the right postcentral gyrus.
30- (C) Typical adolescent gynecomastia that occurs in a large proportion of adolescents and resolves on its own in the majority of them with time.
31- (A) Progressive weakness of the proximal and distal muscles, double vision, eyelid drooping + mediastinal mass--> myasthenia gravis which is commonly associated with thymic hyperplasia/thymoma. It is caused by auto-Abs that block the A.Ch. receptors at the motor end plate.
32- (C) The pic shows severe vertebral osteoporosis with a compression fracture, the most plausible answer is IL-1 since it activates osteoclasts and is increased in postmenopausal osteoporosis which is characterized by increased resorption.
33- (E) The key sentence here is “her symptoms become much more pronounced as the day progresses” which is typical of MG, none of the other choices would cause that. Besides, having normal residual volume excludes the obstructive lung diseases (alpha 1-antitrypsin and chronic bronchitis).
34- (D) Nodular infiltrates + hilar adenopathy + noncaseating granulomas--> classical sarcoidosis.
35- (C) Most probably a case of metabolic syndrome, these patients have dyslipidemia which is characterized by increased triglycerides and FFAs, and decreased HDL cholesterol.
36- (C) The T4-binding substance in the blood is Thyroid binding globulin (TBG). Since Thyroid hormone is a steroid (lipid-soluble), it traverses the cell membrane and acts intracellularly on a nuclear receptor.
37- (A) Patients with Gilbert syndrome are asymptomatic, they may suffer mild jaundice in cases of stress and infection like that case, the jaundice is due to the decreased capacity of the glucuronyl-transferase enzyme, therefore the jaundice would be caused by unconjugated bilirubin. Normal liver enzymes exclude choices B and E, choices C and D should have been accompanied by other signs of anemia (C) or liver failure (D).
38- (F) One of the most dangerous infections in DM that occurs specially after DKA is mucormycosis, the fungus gains access through the cribriform plate and may spread to the orbit and the brain, it causes a necrotizing inflammation, hence the black eschar.
39- (E) A classical case of rheumatoid arthritis, the pathology involves granulomatous inflammation in the synovium of the joints, the reactive synovium forms a mass called “pannus” that destroys the joint and ends up in fibrosis causing the various deformities seen in RA.
40- (A) Type II error (beta error) is calculated by the equation (beta=1 – power), therefore beta equals 0.2 in trial X and 0.1 in trial Y, that is, as the power increases the likelihood of the error decreases.
41- (D) In people with DM increased glucose leads to its increased conversion to sorbitol by the enzyme aldose reductase which is found in the lens, the problem with sorbitol is that it can’t cross the cell membrane, so it gets trapped inside the cell, and it draws water because it is osmotically active, this leads to opacification of the lens and cataract formation.
42- (E) A classical presentation of sickle cell anemia causing acute chest syndrome which is a form of sickle cell crisis. The substitution of glutamic acid with valine in the B-chains leads to polymerization of the Hb under hypoxic conditions forming insoluble polymers, due to this the RBCs become sickle shaped and sticky and they clog the small capillaries leading to ischemia in many organs which leads to the crisis.
43- (B) The carbonic anhydrase inhibitor (acetazolamide) is of benefit in high altitude sickness because it causes acidosis, which counteracts the alkalosis caused by hyperventilation, however it is also a diuretic, and so it would cause some hypovolemia in normotensive persons which can lead to orthostatic hypotension. The only other choice that can cause orthostatic hypotension is impaired sympathetic activity, but it is unrelated to acetazolamide.
44- (B) The sequence (AATAAA) which is transcribed into (AAUAAA) is the signal required to start adenylation and formation of the poly A tail, and it is located downstream (3’) of the coding region, the function of the tail is to protect the mRNA from cleavage, in its absence most of the mRNA would be broken down by the endonucleases in the nucleus.
45- (E) Classical presentation of gestational trophoblastic disease (GTD) characterized by hyperemesis gravidarum, a uterus that’s large for the gestational age, and markedly increased levels of HCG. It is due to abnormal proliferation of the trophoblastic tissue.
46- (B) From the “blistering” diseases the one that most commonly involves the mouth is pemphigus vulgaris; it is caused by auto-Abs to the desmosomes between the keratinocytes in the stratum spinosum layer of the epidermis.
47- (B) He has multiple risk factors; being male, above 45 y/o, living alone, and having major illness.
48- (C) The IIB/IIIA receptor on platelets is the receptor that binds fibrinogen and it is essential for the process of platelet adhesion and aggregation and to strengthen the blood clot.
49- (B) Except for the glucagon receptor, all the other choices are common to both glucagon and epinephrine because both act to initiate the G-protein sequence that ends up in activating glycogen phosphorylase and breaking down glycogen.
50- (C) Tyrosine kinases is a family of enzymes that act as downstream effectors of various growth factors, they function through phosphorylating tyrosine residues on different proteins, since it is a missense mutation (i.e. it didn’t lead to a premature termination of translation, so didn’t affect the amount of the enzyme formed) it probably led to the formation of a non-functional enzyme that can’t phosphorylate.
|* Re:NBME 13 answer key
||***** Correction *****
Block 1 q10, the correct answer is (A) alcohol dehydrogenase. Although both alcohol dehydrogenase and formaldehyde dehydrogenase are involved in the metabolism of methanol and inhibiting any one of them would treat methanol toxicity, the available drug for treating the toxicity (fomepizole) actually inhibits alcohol dehydrogenase.
|* Re:NBME 13 answer key
||I am really sorry for that long delay, I hope the answers will be helpful for everyone, please feel free to review them and for any mistakes
|* Re:NBME 13 answer key
||Missing Q's from Block 1:
A retrospective study is conducted to assess the incidence and outcome of subarachnoid hemorrhage in a midwestern state. The annual incidence of this condition is 15 per 100,000 people and the case fatality rate is 40%. Based on these data, which of the following represents the annual mortality rate for subarachnoid hemorrhage per 100,000 people in this state?
Ans: A) 0.4*15
A 54-year-old man comes to the physician because of a 2-week history of burning epigastric pain. He is recently divorced. His diet mainly consists of fast food. He was treated for H. pylori infection 1 year ago. He uses high doses (600mg daily) of over-the-counter ibuprofen for chronic joint pain. Abdominal examination shows tenderness to deep palpation of the epigastric area. A peptic ulcer is suspected. Which of the following is the strongest predisposing risk factor for this patient's condition?
A) High-fat diet
B) Ibuprofen use
C) Ingestion of alcohol
D) Recent psychosocial stressor
E) Smoking cigars
Ans: Not D because I got that wrong. Any other suggestions?
A 9-year-old girl is brought to the ED by her father because of severe pain in her right shoulder after a fall 1 hour ago. Physical examination shows pain on movement of the right shoulder and a tender right clavicle. An X-ray of the shoulder shows a nondisplaced fracture of the right clavicle. Which of the following structures of the clavicle will most likely assist in producing new bone to heal this fracture?
B) Haversian canal
E) Volkmann canal
And: D) Periosteum
Missing Q's from block 2:
A 60-year-old man comes to the physician because of a 2-week history of fatigue and exercise intolerance. One month ago, he was diagnosed with stage 1 HTN and began treatment with propranolol. His pulse is 56/min, compared with 72/min 1 month ago. His treatment is switched to pindolol. His symptoms resolve within 1 month, and his pulse is 68/min. Which of the following mechanisms of action of pindolol best explains its effect on this patient's heart rate?
A) Competitive agonism
B) Competitive antagonism
C) Inverse agonism
D) Partial agonism
Ans: D) partial agonism
An investigator studying the molecular events in the underlying causes of an autoimmune disease develops a collection of monoclonal antibodies to ribosomal proteins. One of the monoclonal antibodies is found to inhibit the ribosome peptidyl transferase. Which of the following is most likely affected in the presence of this antibody?
A) Assembly of 80S ribosomal subunits
B) Attachment of amino acids to tRNA
C) Dissociation of the 80S ribosomes into 60S and 40S subunits
D) Establishment of covalent bonding between amino acids
E) Release of the mRNA from ribosomes
Ans: D) Establishment of covalent bonding between amino acids
A 9-year-old boy is brought to the ED because of fever, chest pain, and migratory joint pain in his shoulders, hips, and knees for two days. Four weeks ago, he had a febrile pharyngitis, which resolved 2 weeks without treatment. His temperature is 39C. The lungs are clear to auscultation. A pericardial friction rub and quiet heart sounds are heard. Throat cultures do not grow any pathogens. Laboratory testing shows increased antibody titers to streptolysin O. The greatest risk for death at this time is from which of the following?
A) Aortic stenosis
C) Mitral insufficiency
E) Septic shock
Ans: D) Myocarditis
A young adult couple has been unable to conceive for the past two years. The woman has regular menstrual cycles and takes no contraceptives. A semen analysis shows:
Quality: Normal range
Quantity: Normal range
Fructose: 5% of normal content
The most likely cause of this couple's infertility is deficient activity of which of the following in the man?
B) Bulbourethral glands
D) Seminal vesicles
Ans: D) Seminal vesicles
|* Re:NBME 13 answer key
||Also, corrections to the initial post (I don't know if anyone else has brought this up already)
19 - B - Interferon-gamma receptor deficiency
46 - A - adhesins
26 - E - inability to produce hydroxy-halide radicals
3 - C - leukotrienes
3 - E - interferes with translocation
10 - C - microscopic examination of the stool for ova and parasites
42 - E - polymerization of hemoglobin with hypoxic conditions due to amino acid substitution in the beta chain