An Unusual Case of a Hemolytic Crisis associated with the Initiation of an Aromatase Inhibitor in a Patient with Known History of Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal Nocturnal Hemoglobinuria (PNH) is a rare hemolytic disorder characterized by partial or complete absence of the glycosylphosphatidylinositol-anchored proteins (GPI-AP) on the cell membrane of erythrocytes, platelets, and granulocytes rendering them vulnerable to destruction by the complement system. Various medications can provoke hemolytic crises in PNH or healthy subjects. Aromatase inhibitors (AI), which have revolutionized breast cancer management, are not known to trigger hemolytic crises. We report on a case of a 70-year-old female with PNH who was also diagnosed with breast cancer. Following lumpectomy and adjuvant radiation therapy, she was started on an AI to decrease risk of breast cancer recurrence. A few weeks later, she developed malaise, insomnia, and gross hematuria. Diagnostic workup including flow cytometry revealed a hemolytic crisis related to her PNH. An exhaustive investigation to uncover a potential mechanism that may explain the relation between AI initiation and onset of hemolytic crisis was unrevealing.