A 31-year-old woman, G1P0, at 33 weeks gestation presents to the emergency department with… — USMLE Step 3

A $31$ -year-old woman, G1P0, at $33$ weeks gestation presents to the emergency department with severe right upper quadrant abdominal pain and nausea for the past $6$ hours. Her blood pressure is $168/110\text{ mm Hg}$ , and pulse is $98/\text{min}$ . Physical examination reveals marked tenderness over the liver. Fetal heart rate monitoring is reassuring.

Laboratory studies show:
- Hemoglobin: $8.8\text{ g/dL}$
- Platelets: $55,000/\text{mm}^3$
- Aspartate aminotransferase (AST): $480\text{ U/L}$
- Alanine aminotransferase (ALT): $510\text{ U/L}$
- Lactate dehydrogenase (LDH): $950\text{ U/L}$
- Total bilirubin: $2.2\text{ mg/dL}$
- Prothrombin time (PT): $11.5\text{ seconds}$ (Normal: $11-14\text{ seconds}$ )
- Partial thromboplastin time (aPTT): $30\text{ seconds}$ (Normal: $25-40\text{ seconds}$ )

A peripheral blood smear reveals numerous fragmented red blood cells.

Which of the following cellular or histologic processes most accurately describes the primary mechanism of hepatic injury in this patient?

Ischemic coagulative necrosis resulting from sinusoidal fibrin depositionAnswer
B
Centrilobular necrosis driven by free radical-mediated lipid peroxidation
C
Primary failure of hepatic coagulation factor synthesis leading to parenchymal hemorrhage
D
Widespread hepatocyte apoptosis mediated by CD8+ cytotoxic T lymphocytes
E
Microvesicular steatosis due to mitochondrial beta-oxidation dysfunction

Answer

Ischemic coagulative necrosis resulting from sinusoidal fibrin deposition

The correct answer identifies that the hepatic injury in HELLP syndrome is caused by ischemic coagulative necrosis resulting from sinusoidal fibrin deposition. Systemic endothelial injury leads to platelet activation and fibrin microthrombi formation. When these lodge in the hepatic sinusoids, they obstruct blood flow, resulting in focal ischemic necrosis, stretching of Glisson's capsule, and the characteristic right upper quadrant pain and elevated transaminases.

Step-by-Step Solution

Analyze the patient's clinical presentation.

The patient is a pregnant woman in the third trimester presenting with severe hypertension and right upper quadrant pain.

This establishes a differential diagnosis of pregnancy-related complications such as severe preeclampsia, HELLP syndrome, or Acute Fatty Liver of Pregnancy (AFLP).

Interpret the laboratory and peripheral smear findings.

Labs show a microangiopathic hemolytic anemia (anemia, schistocytes, elevated LDH and bilirubin), severe thrombocytopenia, elevated transaminases, and normal coagulation times (PT/aPTT).

These findings are required to confirm the specific diagnosis within the preeclampsia spectrum.

Synthesize the findings to establish a diagnosis.

The combination of Hemolysis, Elevated Liver enzymes, and Low Platelets with normal PT/aPTT definitively points to HELLP syndrome rather than AFLP or DIC.

Normal PT/aPTT distinguishes HELLP from AFLP and DIC, both of which typically present with consumptive coagulopathy and prolonged PT/aPTT.

Identify the primary cellular or histologic mechanism of hepatic injury for the diagnosed condition.

Systemic endothelial injury in HELLP syndrome leads to microvascular thrombosis and fibrin deposition in the hepatic sinusoids, causing focal ischemic coagulative necrosis.

This directly answers the prompt's question regarding the subcellular mechanism of the observed hepatic injury.

Key Concept

HELLP syndrome is characterized by systemic endothelial dysfunction leading to microangiopathic hemolytic anemia and the deposition of fibrin microthrombi in hepatic sinusoids, which subsequently causes ischemic coagulative necrosis of hepatocytes.

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