| * Some NBME 15 questions
||Needless to say if you plan on doing it, don't look thru these.
1. A 3-year-old girl is brought to the physician because of a 1-year history of short stature. She has no history of major medical illness. She is below the 3rd percentile for height and at the 10th percentile for weight. Physical examination shows coarse facial features and contractures of the large joints. X-rays show dysostosis multiplex. Plasma lysosomal enzyme analysis shows increased B-hexosaminidase, [3-glucuronidase, B-galactosidase, and d-fucosidase activities. Which of the following mechanisms is the most likely cause of the lysosomal enzyme findings in this patient‘?
A) Abnormal targeting of these enzymes to lysosomes
B) Deficiency of the other lysosomal enzymes in the cytoplasm
C) Degradation of these enzymes within the cytoplasm
D) Degradation of these enzymes within the lysosomes
E) Storage of these enzymes within the cytoplasm
2. A 20-year-old competitive cyclist taking recombinant human erythropoietin has polycythemia. Which of the following is the most likely cause?
A) Early release of reticulocytes from bone marrow
B) Increased erythrocyte life span
C) Proliferation of bone marrow stem cells
D) Proliferation of erythroid precursors
3. A 25-year-old primigravid woman at 12 weeks‘ gestation comes to the physician 1 hour after she passed a small amount of tissue vaginally at home. Gross examination of this tissue shows an obvious fetus. Microscopic examination of tissue
obtained via dilatation and curettage shows chorionic villi with focal edema and trophoblastic proliferation. Which of the following is the most likely diagnosis?
B) Complete hydatidiform mole
C) Partial hydatidiform mole
D) Placenta accreta
E) Placental site trophoblastic tumor
4. A study is conducted to evaluate the effectiveness of cough medication in children. A total of 120 patients under the age of 12 years who have been diagnosed with a viral upper respiratory tract infection are randomly selected to receive dextromethorphan or no treatment. The participants were recruited from several emergency departments in an urban area. Parents complete a rating scale for their children's cough at baseline and 1 day after receiving dextromethorphan or nothing. The results show a statistically significant improvement in cough scores for patients receiving dextromethorphan
(p=0.04) compared with children receiving no treatment. Which of the following is the most significant limitation to the internal validity of this study?
A) Lack of blinding between groups
B) Limited number of participants
C) Marginal statistical significance
D) Study location limited to only emergency departments
E) Subjective nature of the survey instrument
5. A 40-year-old woman with breast cancer is brought to the physician because of a 1-week history of progressive loss of peripheral vision to the left in both eyes. On examination of each eye, she is unable to count fingers or detect finger movements on the left. An MRI of the brain is most likely to show a metastatic tumor in which of the following locations?
A) Occipital lobe B) Optic chiasrn C) Optic nerve D) Parietal lobe E) Temporal lobe
6. A 54-year-old woman comes to the physician because of a 2-week history of heavy vaginal bleeding. Menopause occurred 5 years ago. She underwent a mastectomy 3 years ago for estrogen receptor-positive breast carcinoma with axillary lymph node involvement. She has been taking tamoxifen, a drug that blocks estrogen receptors in breast
tissue, for the past 3 years. Biopsy of endometrial tissue shows hyperplasia. Which of the following best explains the development of endometrial hyperplasia in this patient?
A) Endometrial tissues become hyperplastic in the absence of estrogen
B) The patient has been noncompliant in taking the estrogen receptor antagonist
C) The patient's breast cancer has metastasized to the patient's uterus
D) The patient's breast cancer is associated with an estrogen-secreting ovarian cancer
E) The patient's medication has an agonist effect on endometrial estrogen receptors
F) The patient's serum estrogen concentrations are increased due to ectopic production of human chorionic gonadotropin
7. A 2-month-old girl is brought to the physician for a follow-up examination 2 days after a complete blood count was found to be abnormal. Her blood group is A, Rh-positive. She was born at term to a healthy 23-year-old woman whose blood group is O, Rh-positive. Birth weight was 3890 g (8 lb 9 02). Pregnancy and delivery were uncomplicated. The patient has been active and feeding well. Her temperature is 37.6°C (99.7°F), pulse is 120/min, and respirations are 30/min. Physical examination shows no abnormalities. Laboratory studies done since birth are shown.
Patient Age 24 Hours
Hemoglobin (g/dL) (N=1 1-15) 16.9
Hematocrit (%) 51
Leukocyte count (Imm3) (N=5000-19,500) 17,200
Segmented neutrophils 4%
Platelet count (Imm 3) (N=150,000—400,000) 185,000
Hemoglobin (g/dL) (N=1 1-15) 15.7
Hematocrit (%) 49
Leukocyte count (Imm3) (N=5000-19,500) 15,600
Segmented neutrophils 3%
Platelet count (Imm 3) (N=150,000—400,000) 198,000
Hemoglobin (g/dL) (N=1 1-15) 12.7
Hematocrit (%) 39
Leukocyte count (Imm3) (N=5000-19,500) 12,900
Segmented neutrophils 5%
Platelet count (Imm 3) (N=150,000—400,000) 205,000
Which of the following is the most likely diagnosis?
A) Alloimmune hemolytic disease of the newborn
B) Congenital cytomegalovirus infection
C) Congenital neutropenia
D) DiGeorge syndrome
E) Severe combined immunodeficiency
8. A 13-year-old boy is scheduled to receive chemotherapy for a leukemia that has the histologic features of malignant lymphocytes. This neoplasm is further typed for cell surface and intracellular markers specific for lymphocyte subsets. The neoplastic cells do not express the following markers: CD4, CDB, surface lgM, surface lgG, cytoplasmic lgM and u-heavy chain, cytoplasmic I96, and Y-heavy chain. The leukemic cells express class I MHC molecules and show rearrangement of the T-lymphocyte receptor B-chain gene D and J segments. Which of the following is the normal counterpart of these malignant lymphocytes?
A) Activated cytolytic effector T lymphocytes in the circulation
8) Mature lgM-secreting B lymphocytes in the lymph node
C) Mature immunoglobulin-secreting plasma cells in the lymph node
D) Pre-B lymphocyte progenitor of mature B lymphocytes in the bone marrow
E) T-Iymphocyte thymocytes localized to the thymic cortex
9. A 56-year-old woman is brought to the emergency department by her husband because of fever and shortness of breath for 2 hours. Her husband says that she also has had urinary frequency and pain with urination for 2 days. She is in respiratory distress. Her temperature is 38.7°C (101 pulse is 120/min, respirations are 30/min, and
blood pressure is 80/50 mm Hg. Which of the following components of the causal organism is the most likely cause of the hypotension?
A) Flagellar H antigen
C) P pilus
D) Polysaccharide capsule
E) Shiga-Iike cytotoxin
10. A newborn undergoes surgical repair of esophageal atresia. Pathologic examination of resected tissue shows that the esophagus is and has no lumen. Which of the following embryonic germ layers is the most likely origin of the cells that fill the lumen?
B) Intermediate mesoderm
C) Neural crest
D) Paraxial mesoderm
E) Surface ectoderm
11. A 50-year-old man comes to the physician because of a 2-week history of progressive shortness of breath while climbing stairs to his office every morning. He reports no other problems, but he is concerned because his father had a major myocardial infarction at the age of 52 years. His pulse is 110/min and regular, respirations are 16/min, and blood pressure is 135/95 mm Hg. The lungs are clear to auscultation. Cardiac examination shows normal heart sounds with a physiologic split of 82. Stress echocardiography shows hypokinesis of the posterior left ventricle with increasing activity levels. Which of the following is the most likely cause of the posterior left ventricular findings in this patient?
A) Disruption of the sympathetic nerves to the left ventricle
B) Extravascular compression of the coronary arteries
C) Increased left ventricular end-diastolic pressure
D) Increased myocardial oxygen consumption
E) Stenosis of the right coronary artery
12. A 75-year-old woman comes to the physician because of a 3-month history of an enlarging lesion on her face. Physical examination shows a 1.5-cm, brown-black, mottled, scaly lesion with irregular borders. Microscopic
examination of a biopsy specimen of the lesion shows atypical melanocytes spread along the basilar layer of the epidermis. Which of the following is the most likely cause of these findings?
A) Acanthosis nigricans
B) Actinic keratosis
C) Compound nevus
D) Lentigo maligna
E) Seborrheic keratosis
13. A 59-year-old man comes to the physician because of a 10-day history of shortness of breath, fatigue, and cough. His respirations are 12/min. The lungs are clear to auscultation and percussion. Laboratory studies show:
Hemoglobin 11.8 g/dL
Leukocyte count 146,400/mm3
Segmented neutrophils 47%
Other cells 4%
Platelet count 804,000/mm3
Which of the following is the most appropriate pharmacotherapy for this patient?
A) Anti-interleukin-S (IL-5) B) Cytarabine
E) Interferon alfa
14. An investigator wishes to test the hypothesis that a number of CD44 splice variants correlate with aggressive disease progression and risk of relapse in patients with Hodgkin disease, especially if the variant protein CD44v10 is expressed. The investigator plans to retrospectively screen archives of fresh frozen tissue and paraffin-embedded biopsy specimens from documented Hodgkin disease patients. Assuming the necessary reagents are available, which of the following methods would be the most effective in screening the archives for the variant protein?
A) Affinity column chromatography
B) Density gradient oentrifugation
D) Northern blot
E) Polymerase chain reaction (PCR)
F) Reverse transcriptase PCR
G) Southern blot
15. A 75-year-old woman is brought to the physician because of a 1-day history of fever and back pain. Her temperature is 395°C (103.1°F), pulse is 111/min, respirations are 32/min, and blood pressure is 115/79 mm Hg. Physical examination shows left-sided costovertebral angle tenderness. Laboratory studies show a leukocyte count of 17,000/mm3 (with 9% bands) and pyuria. Urine cultures grow Escherichia coli. It is determined that the patient's fever is partially due to interleukin-6 (IL-6), which was induced by the lL-1 produced during the immune response. Which of the following best describes the role of IKB in the nuclear factor-kappa B (NF-KB) signal transduction pathway from IL-1 binding to IL-6 induction in this patient?
A) Attaches to cytokine receptor
B) Facilitates proteolytic cleavage of NF-KB dimers
C) Phosphorylates NF-KB
D) Releases NF-KB after undergoing phosphorylation
E) Translocates to the nucleus after undergoing phosphorylation
16. Which of the following best explains why deoxygenated blood can carry more carbon dioxide for a given Poo2 than oxygenated blood?
A) Deoxyhemoglobin does not bind to 2,3-bisphosphoglycerate as efficiently as oxyhemoglobin
B) Deoxyhemoglobin has a lower capacity to form carbamino compounds than oxyhemoglobin
C) Deoxyhemoglobin has a lower pKa than oxyhemoglobin
D) Deoxyhemoglobin is a better buffer of hydrogen ions than oxyhemoglobin
E) Oxygen and carbon dioxide compete for the same binding site in hemoglobin
F) Oxyhemoglobin binds nitric oxide with a higher affinity than deoxyhemoglobin
17. A 3-year-old boy with chronic otitis media is scheduled to undergo bilateral myringotomies with placement of
polyethylene tubes under general anesthesia. He is asleep after only three to five breaths of inhalational anesthetic delivered by face mask. Which of the following properties of the anesthetic is the most likely explanation for the rapid onset of action?
A) High blood solubility
B) High hepatic metabolism
C) High minimum alveolar concentration
D) Low blood solubility
E) Low hepatic metabolism
F) Low minimum alveolar concentration
18. An investigator is studying Helicobacter pylori strains isolated from the same patient over several years. The immune response to proteins produced by these strains is observed. It is found that the original H. pylori isolate from the patient expresses one protein recognized by the patient's antibodies, but subsequent isolates do not express this protein. Sequencing of the gene encoding the protein from the original and subsequent isolates is done. It is found that subsequent isolates have nine consecutive cytidine residues, whereas the original isolate has eight. The results are shown.
...ACC CCC CCC ACT CAA ATT GAA CCT AGC...
...Thr Pro Pro Thr Gln lle Glu Pro Ser...
ACC CCC CCC CAC TCA AAT TGA ACC TAG
...Thr Pro Pro His Ser Asn STOP
Which of the following mechanisms best explains this genetic change?
A) Crossing over
B) DNA excision repair
C) Slipped-strand mispairing
D) Thymidine dimer formation
E) Transposon insertion
19. During a series of normal skeletal muscle twitches, the ATP concentration does not fall appreciably because of
which of the following?
A) ATP is hydrolyzed only during relaxation
B) ATP is quickly regenerated from creatine phosphate
C) Creatine phosphate is hydrolyzed by myosin
D) The initial ATP concentration is high
20. A 6-year-old boy with severe mental retardation and choreoathetosis is being evaluated for Lesch-Nyhan syndrome. Leukocytes are obtained for an assay of hypoxanthine-guanine phosphoribosyltransferase at saturating concentrations of phosphoribosylpyrophosphate and varying concentrations of guanine. Results of the data are shown.
Guanine Velocity (Patient) (mM) pmoleslmin 0.06 0.26
Which of the following is the approximate Michaelis constant Km] (in mM) for guanine in this patient?