Differential diagnosis Practice Questions

Question 1

A scientist in Chicago is studying a new blood test to detect Ab to EBV with increased sensitivity and specificity. So far, her best attempt at creating such an exam reached 82% sensitivity and 88% specificity. She is hoping to increase these numbers by at least 2 percent for each value. After several years of work, she believes that she has actually managed to reach a sensitivity and specificity much greater than what she had originally hoped for. She travels to China to begin testing her newest blood test. She finds 2,000 patients who are willing to participate in her study. Of the 2,000 patients, 1,200 of them are known to be infected with EBV. The scientist tests these 1,200 patients' blood and finds that only 120 of them tested negative with her new exam. Of the patients who are known to be EBV-free, only 20 of them tested positive. Given these results, which of the following correlates with the exam's specificity?

Accepted Answer

98%

Answer

82%

Answer

90%

Answer

84%

Answer

86%

Question 2

A group of neurologists develop a new blood test for Alzheimer's. They are optimistic about the test, as they have found that for any given patient, the test repeatedly produces very similar results. However, they find that the new test results are not necessarily consistent with the gold standard of diagnosis. How would this new test most accurately be described?

Accepted Answer

Reliable

Answer

Valid and reliable

Answer

Valid

Answer

Biased

Answer

Neither valid nor reliable

Question 3

A research team develops a new monoclonal antibody checkpoint inhibitor for advanced melanoma that has shown promise in animal studies as well as high efficacy and low toxicity in early phase human clinical trials. The research team would now like to compare this drug to existing standard of care immunotherapy for advanced melanoma. The research team decides to conduct a non-randomized study where the novel drug will be offered to patients who are deemed to be at risk for toxicity with the current standard of care immunotherapy, while patients without such risk factors will receive the standard treatment. Which of the following best describes the level of evidence that this study can offer?

Accepted Answer

Level 3

Answer

Level 1

Answer

Level 5

Answer

Level 4

Answer

Level 2

Question 4

A mother presents to the family physician with her 16-year-old son. She explains, "There's something wrong with him doc. His grades are getting worse, he's cutting class, he's gaining weight, and his eyes are often bloodshot." Upon interviewing the patient apart from his mother, he seems withdrawn and angry at times when probed about his social history. The patient denies abuse and sexual history. What initial test should be sent to rule out the most likely culprit of this patient's behavior?

Accepted Answer

Urine toxicology screen

Answer

Complete blood count

Answer

Sexually transmitted infection (STI) testing

Answer

Blood culture

Answer

Slit lamp examination

Question 5

A 52-year-old man comes to the physician because of a 3-week history of a cough and hoarseness. He reports that the cough is worse when he lies down after lunch. His temperature is 37.5°C (99.5°F); the remainder of his vital signs are within normal limits. Because the physician has recently been seeing several patients with the common cold, the diagnosis of a viral upper respiratory tract infection readily comes to mind. The physician fails to consider the diagnosis of gastroesophageal reflux disease, which the patient is later found to have. Which of the following most accurately describes the cognitive bias that the physician had?

Accepted Answer

Availability

Answer

Framing

Answer

Anchoring

Answer

Visceral

Answer

Confirmation

Question 6

A 27-year-old woman presents to the emergency department complaining of a left-sided headache and right-sided blurry vision. She states that 2 weeks ago she developed dark urine and abdominal pain. She thought it was a urinary tract infection so she took trimethoprim-sulfamethoxazole that she had left over. She planned on going to her primary care physician today but then she developed headache and blurry vision so she came to the emergency department. The patient states she is otherwise healthy. Her family history is significant for a brother with sickle cell trait. On physical examination, there is mild abdominal tenderness, and the liver edge is felt 4 cm below the right costal margin. Labs are drawn as below:

Hemoglobin: 7.0 g/dL
Platelets: 149,000/mm^3
Reticulocyte count: 5.4%
Lactate dehydrogenase: 3128 U/L

Total bilirubin: 2.1 mg/dL
Indirect bilirubin: 1.4 mg/dL
Aspartate aminotransferase: 78 U/L
Alanine aminotransferase: 64 U/L

A peripheral smear shows polychromasia. A Doppler ultrasound of the liver shows decreased flow in the right hepatic vein. Magnetic resonance imaging of the brain is pending. Which of the following tests, if performed, would most likely identify the patient’s diagnosis?

Accepted Answer

Flow cytometry

Answer

Glucose-6-phosphate-dehydrogenase levels

Answer

Anti-histone antibodies

Answer

Bone marrow biopsy

Answer

Hemoglobin electrophoresis

Question 7

A student health coordinator plans on leading a campus-wide HIV screening program that will be free for the entire undergraduate student body. The goal is to capture as many correct HIV diagnoses as possible with the fewest false positives. The coordinator consults with the hospital to see which tests are available to use for this program. Test A has a sensitivity of 0.92 and a specificity of 0.99. Test B has a sensitivity of 0.95 and a specificity of 0.96. Test C has a sensitivity of 0.98 and a specificity of 0.93. Which of the following testing schemes should the coordinator pursue?

Accepted Answer

Test C on the entire student body followed by Test A on those who are positive

Answer

Test A on the entire student body followed by Test B on those who are positive

Answer

Test A on the entire student body followed by Test C on those who are positive

Answer

Test C on the entire student body followed by Test B on those who are positive

Answer

Test B on the entire student body followed by Test A on those who are positive

Question 8

A 27-year-old soldier is brought to the emergency department of a military hospital 20 minutes after being involved in a motor vehicle accident during a training exercise. He was an unrestrained passenger. On arrival, he has shortness of breath and chest pain. He appears pale and anxious. His temperature is 37°C (98.6°F), pulse is 110/min, respirations are 20/min, and blood pressure is 100/65 mm Hg. He is alert and oriented to person, place, and time. Examination shows pale conjunctivae and mucous membranes. There is bruising on the chest, extremities, and abdomen. The lungs are clear to auscultation. He has normal heart sounds and flat neck veins. The abdomen is flat, soft, and mildly tender. The remainder of the physical examination shows no abnormalities. High-flow oxygen is applied, and intravenous fluid resuscitation is begun. A chest x-ray is obtained. Which of the following is the most appropriate next step in management?

Accepted Answer

CT scan of the chest with contrast

Answer

Placement of a chest tube

Answer

Pericardiocentesis

Answer

Abdominal ultrasonography

Answer

Intubation with positive pressure ventilation

Question 9

A trauma 'huddle' is called. Morphine is administered for pain. Low-flow oxygen is begun. A traumatic diaphragmatic rupture is suspected. Infusion of 0.9% saline is begun. Which of the following is the most appropriate next step in management?

Accepted Answer

CT of the chest, abdomen, and pelvis

Answer

Chest fluoroscopy

Answer

Barium study

Answer

MRI chest and abdomen

Answer

ICU admission and observation

Question 10

In a randomized controlled trial studying a new treatment, the primary endpoint (mortality) occurred in 14.4% of the treatment group and 16.7% of the control group. Which of the following represents the number of patients needed to treat to save one life, based on the primary endpoint?

Accepted Answer

1/(0.167 - 0.144)

Answer

1/(0.144 - 0.167)

Answer

1/(0.300 - 0.267)

Answer

1/(0.267 - 0.300)

Answer

1/(0.136 - 0.118)

Differential diagnosis

Study Resources

Lessons

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Lessons

Symptom-based differential diagnosis approach

System-based differential construction

Probability ranking in differentials

Common vs rare disease considerations

Age and demographic considerations

Pattern recognition in diagnosis

Anatomical approach to differential diagnosis

Syndrome recognition

Refinement of differential with testing

Interpreting diagnostic ambiguity

Ruling in vs ruling out strategies

Cognitive biases in differential construction

Integration of diagnostic information

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