Test Taking Skills

Clinical Vignette Examples

How do you sort out the uncommon from the common? Novice students do not have extensive experience in relative frequency or prevalence of disease. However, the old adage that 'common things are common' always applies. Students may fall into the trap of thinking that questions emphasize the rare and unusual, but that is not the case. It is actually quite difficult to write a good question on a rare disease, because the stem has to include sufficient highly specific information to get to the rare diagnosis.

Why do some questions cover rare diseases? Some of them are elegant examples of mechanisms of disease. Some represent life-threatening diseases that should not be missed. The infectious disease physician in Palm Beach who recognized the clues and diagnosed inhalational anthrax back in 2001, without ever having seen a case of anthrax before, performed a remarkable service for public health. As a physician, you are a team leader who is expected to guide others with a broad fund of knowledge.

A 72-year-old man has been feeling tired and lethargic for 5 months. He has noted increasing hesitency with urination. On physical examination his prostate is diffusely enlarged. Laboratory studies show sodium 139 mmol/L, potassium 4.0 mmol/L, chloride 104 mmol/L, CO2 25 mmol/L, creatinine 4 mg/dL, and glucose 81 mg/dL. Which of the following renal abnormalities is most likely to be present in this man?

A. Cortical atrophy

B. Glomerulonephritis

C. Papillary necrosis

D. Polycystic change

E. Renal cell carcinoma

The findings point to prostatic hyperplasia with obstructive uropathy leading to renal cortical atrophy as the cause for his incipient chronic renal failure. That is a common diagnosis, and there is nothing in the stem to point to another cause. None of the other diagnoses are absolutely excluded, they are just less likely in view of the findings given.

A 55-year-old man has had dysuria for the past week. Over the past 2 days he has experienced shaking chills. On physical examination his temperature is 39.3 C.. A urinalysis shows sp gr 1.016, pH 6, 1+ glucose, 1+ blood, no ketones, and no protein. Urine microscopic examination shows numerous WBCs and WBC casts. His serum creatinine is 1.5 mg/dL and glucose 155 mg/dL with hemoglobin A1C 8.7%. A renal ultrasound scan shows a 0.3 cm free floating echodense object in the left renal pelvis. Which of the following complications has this man most likely developed?

A. Cortical atrophy

B. Glomerulonephritis

C. Papillary necrosis

D. Polycystic change

E. Renal cell carcinoma

In this next example we have the same list of foils, but now the findings are those of infection. Yes, this could also stem from urinary tract obstruction from prostatic hyperplasia, but now we have clues of diabetes mellitus (with hyperglycemia) and pyelonephritis with WBC casts. In addition, we have a very distinctive finding: the free floating object. Thus, we can identify risk factors and the consequence of papillary necrosis, an uncommon finding.