We’re back with a USMLE® Step 2 CK Question of the Day! Today’s case involves a 22-year-old man with abdominal pain. Which of the following is the most likely cause of this patient’s condition?
A 22-year-old man comes to the clinic complaining of a 6-week history of intermittent abdominal pain. The patient states the pain is located mainly in the right upper quadrant and typically occurs after meals. The patient denies any past medical history. He states his father had his spleen removed at a young age but is unsure of the details. His vital signs are within normal limits. Physical examination shows mucosal pallor and scleral icterus. There is no pain on palpation of the abdomen. The spleen tip is palpable. Laboratory results are as follows:
| Laboratory value | Result |
| Hematologic | |
| Leukocyte count | 6,000/mm3 |
| Platelet count | 175,000/mm3 |
| Hemoglobin | 10.1 g/dL |
| Mean corpuscular volume (MCV) | 84 fL |
| Mean corpuscular hemoglobin concentration (MCHC) | 40 g/dL |
| Red cell distribution width (RDW) | 15% |
| Reticulocyte count | 8.1% |
Which of the following is the most likely cause of this patient’s condition?
A. Acalculous inflammation of the gallbladder
B. Intermittent common bile duct obstruction with brown pigment gallstones
C. Intermittent gallbladder obstruction with black pigment gallstones
D. Spasm of the biliary tracts secondary to cholesterol stone obstruction
E. Fibrotic and calcified gallbladder
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 2 CK Question is…
C. Intermittent gallbladder obstruction with black pigment gallstones
Before we get to the Main Explanation, let’s see why the answer wasn’t A, B, D, or E. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
Today’s incorrect answers are…
A. Acalculous inflammation of the gallbladder
Incorrect: Acalculous cholecystitis is an acute inflammatory disorder of the gallbladder that is most commonly seen in conditions that cause biliary stasis, such as in critically ill patients (e.g., multiorgan failure, post-surgery, trauma) or those on prolonged total parenteral nutrition (TPN). Patients typically present with fever and persistent right upper quadrant pain, neither of which are seen in this patient.
B. Intermittent common bile duct obstruction with brown pigment gallstones
Incorrect: Brown pigment stones are associated with bacterial (e.g. E. coli) or parasitic (e.g. liver fluke) infections of the biliary system. Brown pigment stones are prevalent in Asian countries but are rarely seen in patients in the United States. Additionally, this patient’s underlying condition predisposes him to a different type of stone composition.
D. Spasm of the biliary tracts secondary to cholesterol stone obstruction
Incorrect: Spasm of the biliary tract secondary to obstruction of the common bile duct is seen in patients with choledocholithiasis. Although cholesterol gallstones are the most common stones found in the gallbladder, this patient’s underlying condition predisposes him to a different type of stone composition.
E. Fibrotic and calcified gallbladder
Incorrect: Porcelain gallbladder refers to a fibrotic and calcified gallbladder that occurs after recurrent episodes of cholecystitis. Although this patient’s current condition may predispose him to develop a porcelain gallbladder, it most commonly presents much later in life (usually around the 6th decade).
Main Explanation
This young adult, who presents with complaints of postprandial right upper quadrant (RUQ) pain and laboratory results showing anemia and elevated mean corpuscular hemoglobin concentration (MCHC), likely has black pigment gallstone formation secondary to hereditary spherocytosis (HS).
Black pigment gallstones form when the bile contains a high concentration of unconjugated bilirubin in the bilirubin tree, such as in patients with chronic extravascular red cell hemolysis. This can be seen in patients with sickle cell disease or hereditary spherocytosis. Brown pigment stones, on the other hand, can precipitate when the biliary tract is infected by certain microbes (e.g., E. coli, Clonorchis sinensis) that produce β-glucuronidase, an enzyme that unconjugates previously conjugated bilirubin. Unconjugated bilirubin is water insoluble and combines with calcium to form brown pigment stones.
However, the most common gallstones are cholesterol stones. Bile formation is the only significant pathway for the body to eliminate excess cholesterol, either as free cholesterol or as bile salts. Cholesterol becomes water-soluble when combined with bile salts; therefore, when cholesterol concentrations exceed the solubility capacity of bile salts (supersaturation), cholesterol stones can form. Conditions that increase cholesterol synthesis (e.g., obesity, medications such as fibrates) or decrease bile salt formation (e.g. malabsorptive conditions) predispose individuals to forming gallstones. Additionally, hypomotility of the gallbladder results in bile stasis, which also promotes gallstone formation (e.g., pregnant women, patients on total parenteral nutrition). This patient did not have risk factors for cholesterol stones. Instead, his physical exam and laboratory values suggested a risk for pigment stones.
Major takeaway
Black pigment gallstones can be seen in patients with chronic hemolytic conditions, whereas brown pigment gallstones are formed in patients with an infection of the biliary tree. Cholesterol gallstones precipitate in the gallbladder in conditions that cause increased cholesterol synthesis or decreased bile salt formation.
References
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