A 30-year-old woman with known sickle cell disease presents with sudden onset severe back pain and priapism. Her crisis is best explained by the pathophysiological mechanism of:

• A Intravascular hemolysis releasing free hemoglobin that scavenges nitric oxide
• B Splenic sequestration of sickled cells causing acute-on-chronic anemia
• C Complement-mediated destruction of sickled cells
• D Polymerization of HbS under deoxygentation causing RBC sickling and vaso-occlusion ✓

Explanation

The fundamental mechanism of vaso-occlusive crisis is deoxy-HbS polymerization, forming long fibers that distort the RBC into a rigid sickle shape. These cells occlude small vessels, causing ischemic pain in bones, organs, and other tissues including the corpus cavernosum (priapism). While nitric oxide scavenging contributes to some complications, vaso-occlusion is the direct cause of this presentation. Splenic sequestration causes sudden splenomegaly and anemia in young children; complement is not the primary mechanism.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.