## Complement Inhibition in Atypical HUS **Key Point:** Eculizumab is the gold-standard drug of choice for aHUS, particularly in cases with genetic complement dysregulation (Factor H, Factor I, C3 mutations). It blocks C5 and prevents terminal complement-mediated thrombotic microangiopathy. ### Pathophysiology of aHUS 1. Genetic mutations in complement regulatory proteins (Factor H, Factor I, C3, etc.) 2. Uncontrolled alternative pathway activation 3. Endothelial cell injury and platelet consumption 4. Microthrombi formation in renal microvasculature 5. Hemolysis, thrombocytopenia, and acute kidney injury **High-Yield:** Eculizumab is now the standard of care for aHUS because: - Directly blocks complement-mediated endothelial damage - Effective even when plasma exchange has failed - Prevents progression to end-stage renal disease - FDA-approved specifically for aHUS ### Treatment Algorithm for aHUS ```mermaid flowchart TD A[aHUS diagnosed]:::outcome --> B[Plasma exchange initiated]:::action B --> C{Response to PE?}:::decision C -->|Yes| D[Continue PE, supportive care]:::action C -->|No| E[Add Eculizumab]:::action E --> F[C5 inhibition + PE]:::action F --> G[Hematologic remission]:::outcome G --> H[Continue Eculizumab long-term]:::action ``` **Clinical Pearl:** Factor H mutations account for ~30% of aHUS cases. In these patients, eculizumab provides superior outcomes compared to plasma exchange alone, with remission rates >80%. **Warning:** Conventional immunosuppressants (corticosteroids, cyclophosphamide) are ineffective in aHUS because they do not address the underlying complement dysregulation.
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