A 30-year-old woman develops hemolytic anemia, thrombocytopenia, and a rash following methyldopa therapy. The underlying mechanism of drug-induced autoimmune hemolytic anemia in this case involves:

• A Drug acting as hapten on RBC surface, inducing anti-drug antibodies (type II hypersensitivity)
• B Formation of drug-anti-drug immune complexes that deposit on RBCs (innocent bystander mechanism)
• C T cell-mediated direct destruction of opsonized RBCs
• D Methyldopa modifying RBC membrane proteins or inducing loss of tolerance, generating true anti-RBC autoantibodies ✓

Explanation

Methyldopa (and procainamide) cause drug-induced AIHA via an 'autoantibody' mechanism — the drug modifies the Rh antigen complex or otherwise breaks peripheral tolerance, generating antibodies that react with native RBC antigens even in the absence of drug. Unlike the hapten mechanism (penicillin) or immune-complex mechanism (quinine), these antibodies are directed against intrinsic RBC determinants and the DAT is positive with anti-IgG alone. This mechanism explains why hemolysis can persist for months after drug withdrawal.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.