2024 USMLE Practice Paper 3

1. A 30-year-old woman presents with infertility, irregular periods, and hirsutism. Ultrasound shows enlarged ovaries with multiple cysts. Which of the following is most consistent with her diagnosis?

A. Primary ovarian insufficiency
B. Hypogonadotropic hypogonadism
C. Polycystic ovary syndrome
D. Premature menopause
E. Clear cell adenocarcinoma

Correct Answer: C

Notes:

The clinical presentation of infertility, irregular periods, hirsutism, and ultrasound findings of enlarged ovaries with multiple cysts are indicative of polycystic ovary syndrome (PCOS). PCOS is characterized by the dysregulation of ovarian steroidogenesis and hyperandrogenism.

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2. A 60-year-old man presents with a history of premature coronary artery disease. His lipid profile shows markedly elevated low-density lipoprotein (LDL) cholesterol. Genetic testing reveals a mutation affecting the LDL receptor. Which type of familial dyslipidemia is most likely in this patient?

A. Type I familial dyslipidemia
B. Type II familial dyslipidemia
C. Type III familial dyslipidemia
D. Type IV familial dyslipidemia
E. Type V familial dyslipidemia

Correct Answer: B

Notes:

Type II familial dyslipidemia, or familial hypercholesterolemia, is characterized by genetic mutations affecting the LDL receptor. This causes markedly elevated LDL cholesterol levels and a higher risk of coronary artery disease. Type I involves LPL deficiency, Type III involves apoE defects, Type IV involves VLDL overproduction, and Type V involves increased chylomicrons and VLDL.

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3. A 40-year-old asplenic patient presents with fever and rusty-colored sputum. Chest X-ray reveals a lobar consolidation. Which of the following vaccinations would have best prevented this condition?

A. Hib vaccine
B. Influenza vaccine
C. Meningococcal vaccine
D. Pneumococcal polysaccharide vaccine
E. Varicella vaccine

Correct Answer: D

Notes:

The clinical presentation of fever, rusty-colored sputum, and lobar consolidation on chest X-ray is consistent with pneumococcal pneumonia. Streptococcus pneumoniae infections are more common and severe in asplenic patients due to their impaired ability to clear encapsulated organisms. The pneumococcal polysaccharide vaccine (PPSV23) is indicated to prevent such infections. Other vaccines listed do not protect against Streptococcus pneumoniae.

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4. A 35-year-old male presents with loss of visual and auditory reflexes following a severe head injury. The injury most likely affected which part of the brainstem?

A. Superior colliculus
B. Inferior colliculus
C. Pyramidal decussation
D. Pons
E. Superior cerebellar peduncle

Correct Answer: A

Notes:

The superior colliculus is involved in directing eye movements and processing visual stimuli, while the inferior colliculus processes auditory information. Since the patient has lost both visual and auditory reflexes, the superior colliculus is most likely affected. The pyramidal decussation is associated with motor crossing, the pons contains nuclei for cranial nerves V to VIII, and the superior cerebellar peduncle is a major output pathway of the cerebellum.

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5. A 60-year-old female with hypertension has plasma para-aminohippuric acid (PAH) concentration (PPAH) of 0.2 mg/mL, urine PAH concentration (UPAH) of 50 mg/mL, and urine flow rate (V) of 2 mL/min. Which parameter can be estimated using these values?

A. Glomerular filtration rate (GFR)
B. Renal blood flow (RBF)
C. Effective renal plasma flow (eRPF)
D. Plasma volume
E. Cardiac output

Correct Answer: C

Notes:

Effective renal plasma flow (eRPF) can be estimated using PAH clearance, which is calculated as eRPF = UPAH × V / PPAH. In this case, eRPF = 50 mg/mL × 2 mL/min / 0.2 mg/mL = 500 mL/min.

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6. A 68-year-old male is brought to the emergency department with a 2-hour history of left-sided weakness and slurred speech. He has a history of atrial fibrillation, managed with anticoagulants. A non-contrast CT of the head is performed to assess for hemorrhage, which is negative. What is the next best step in the management of this patient?

A. Start intravenous tPA
B. Administer aspirin and clopidogrel
C. Perform thrombectomy
D. Order a diffusion-weighted MRI
E. Begin heparin infusion

Correct Answer: A

Notes:

The patient presents with acute ischemic stroke symptoms and is within the 3-4.5 hour window for intravenous tPA administration, as long as there are no contraindications. While thrombectomy may be considered for large artery occlusion, it is not the immediate next step if tPA administration is indicated and feasible within the time limit. Aspirin and clopidogrel are used for secondary prevention, and MRI would confirm ischemia but would not influence the immediate decision to administer tPA.

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7. A 60-year-old man with a history of chronic kidney disease presents with irritability and stupor. Laboratory tests reveal an elevated serum sodium level. What is the most likely cause of his symptoms?

A. Hyponatremia
B. Hypernatremia
C. Hyperkalemia
D. Hypercalcemia
E. Hypophosphatemia

Correct Answer: B

Notes:

Hypernatremia, or elevated serum sodium, can lead to neurologic symptoms such as irritability and stupor. Hyponatremia often presents with nausea, malaise, and seizures. Hyperkalemia typically causes cardiac abnormalities like wide QRS and peaked T waves, as well as muscle weakness. Hypercalcemia manifests with renal stones, bone pain, abdominal pain, and psychiatric symptoms. Hypophosphatemia leads to bone loss and osteomalacia but does not primarily cause irritability and stupor.

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8. A clinical study reports a 95% confidence interval (CI) for the mean difference in blood pressure between two treatments as (2 mmHg, 10 mmHg). Which statement correctly interprets this finding?

A. The null hypothesis (H0) is not rejected.
B. The results are not statistically significant.
C. The true mean difference is expected to be exactly 6 mmHg.
D. There is a 5% chance that the true mean difference is either less than 2 mmHg or more than 10 mmHg.
E. The null hypothesis (H0) is rejected.

Correct Answer: E

Notes:

The null hypothesis is rejected when the 95% CI for the mean difference excludes 0. In this case, the 95% CI ranges from 2 mmHg to 10 mmHg, which does not include 0, indicating that the results are statistically significant. Option D describes a misinterpretation of the CI, and Options A, B, and C do not accurately reflect the rejection of the null hypothesis and statistical significance.

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9. A 50-year-old woman presents with progressive symmetric proximal muscle weakness, particularly involving her shoulders. Laboratory tests are positive for anti-Jo-1 antibodies, and muscle biopsy shows endomysial inflammation with CD8+ T cells. What is the most likely diagnosis?

A. Polymyositis
B. Dermatomyositis
C. Polymyalgia rheumatica
D. Fibromyalgia
E. Myositis ossificans

Correct Answer: A

Notes:

Polymyositis is characterized by progressive symmetric proximal muscle weakness, especially of the shoulders, and endomysial inflammation with CD8+ T cells. Positive anti-Jo-1 antibodies are specific markers for this condition. Dermatomyositis would additionally involve skin findings, which are not mentioned here.

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10. A 32-year-old woman is diagnosed with a hydatidiform mole. Histological examination reveals some hydropic villi with focal trophoblastic proliferation and the presence of fetal parts. What is the most likely karyotype in this case?

A. 46,XX
B. 46,XY
C. 69,XXX
D. 46,XXY
E. 46,XY

Correct Answer: C

Notes:

The presence of some hydropic villi, focal trophoblastic proliferation, and fetal parts is characteristic of a partial hydatidiform mole. The most common karyotypes for partial moles are triploid, such as 69,XXX or 69,XXY, resulting from fertilization of an egg by two sperm.

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