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Exam Section 1: Item 3 of 50
National Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
3. A 42-year-old man is struck by a motor vehicle. His only injury is a
closed fracture of the proximal tibia. Initial neurovascular examination
shows no deficits. Twenty-four hours later, he has increased leg pain and
paresthesias in the dorsal space between his
first and second toes. The patient begins to pass dark red urine and
becomes oliguric. Urinalysis is positive for blood but no erythrocytes are
seen on microscopic examination. Which of the following acute
disorders is the most likely cause of the renal
failure?
A) Glomerulonephritis
B) Hemolytic-uremic syndrome
C) Interstitial nephritis
D) Nephrotic syndrome
E) Tubular necrosis. Answer: E.
,Tibial fractures present a high risk for compartment syndrome. The
fracture results in blood vessel injury and muscle injury, inflammation,
and edema. Because the fascia containing the anterior compartment of
the leg does not stretch, bleeding and swelling can
cause increased pressure in the compartment. This increased pressure in
turn inhibits venous drainage, further increasing pressure in the
compartment. Eventually the nerve supply and associated arteries are
compromised, leading to the classic signs and
symptoms of compartment syndrome. Signs and symptoms of
compartment syndrome include pain out of proportion to examination
findings, pain with passive movement of the muscles, paresthesia, pallor,
pulselessness, and paralysis. Compromised blood supply
deprives muscle and tissue of oxygen and glucose, leading to tissue
ischemia and necrosis. Muscle necrosis leads to rhabdomyolysis,
myoglobinuria, and acute renal failure. Evaluation of rhabdomyolysis
reveals red or brown urine and urinalysis is typically positive
for blood due to the presence of myoglobinuria without microscopic
evidence of red blood cells. A complication of rhabdomyolysis is acute
kidney injury from acute tubular necrosis secondary to the release of
nephrotoxic myoglobin and nonprotein heme pigments.
Acute tubular necrosis typically occurs following an ischemic or
nephrotoxic insult to the kidneys, which results in loss of the tubular
epithelium. Granular, muddy brown casts are common on urinalysis.
Compartment syndrome is treated by immediate fasciotomy to
decrease compartment pressure and support tissue perfusion.
Incorrect Answers: A, B, C, and D.
,Glomerulonephritis (Choice A) refers to a variety of glomerular
diseases, including nephritic and nephrotic syndromes. Nephritic
syndromes typically present with acute renal failure associated with h
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Exam Section 1: Item 5 of 50
National, Board of Medical Examiners
Comprehensive Basic Science Self-Assessment
5. A 65-year-old woman has ascites. Which of the following additional
findings indicates a diagnosis of constrictive pericarditis rather than
cirrhosis?
O A) Edema of the lower extremities
B) Esophageal varices
C) Hypoalbuminemia
D) Hyponatremia
E) Increased jugular venous pressure
F) Splenomegaly. Answer: E.
Increased jugular venous pressure (JVP) is an expected finding in
constrictive pericarditis (CP) and would not be found in patients with
volume overload secondary to cirrhosis. CP describes a pathologic state
whereby the pericardium, which encases the entirety of
the heart and the origins of the great vessels, loses its elasticity. This can
occur in patients with viral infections, connective tissue disease,
, tuberculosis, or as a result of cardiac surgery or radiation. During the
normal cardiac cycle, increased venous return to the
right atrium (RA) and right ventricle (RV) during inspiration leads to
transient expansion of the RV with slight bowing of the interventricular
septum into the left ventricle (LV). This increased RV preload does not
impair LV filling as the pericardial sac expands to
accommodate the increased RV volume. In constrictive pericarditis, the
pericardial sac loses its elasticity. When venous return to the right heart
increases, the pericardial sac is unable to expand, which exacerbates
movement of the interventricular septum into the
LV. This impairs diastolic filling of the LV and reduces cardiac output.
LV diastolic filling is further reduced by a reduction in preload from the
pulmonary veins. The constricted pericardium does not respond to
normal changes in intrathoracic pressure during
inspiration, but the pulmonary venous system, which lies outside of the
pericardium, experiences a normal drop in pressure during inspiration.
This difference creates an abnormal pressure gradient that reduces LV
preload and leads to reduced cardiac output. The
RV and LV develop interventricular dependence whereby increased
pressure in each ventricle begins to affect the other ventricle. CP
ultimately results in equalization of pressures in all four chambers, with
clinical evidence of right heart failure exhib
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Exam Section 1: Item 4 of 50