The first reported case of concurrent trimethoprim-sulfamethoxazole-induced immune hemolytic anemia and thrombocytopenia.

BACKGROUND: Drug-induced immune hemolytic anemia (DIIHA) and drug-induced immune thrombocytopenia (DIIT) are rare but dangerous complications of pharmacotherapy that may be underrecognized in hematopoietic stem cell transplant (HSCT) patients due to overlap of signs and symptoms with those of more common disease processes. CASE REPORT: A 61-year-old woman with NK-cell deficiency and GATA-2-associated myelodysplastic syndrome, status post-recent allogeneic HSCT (Day +58), presented with 3 days of acute-onset severe back pain, muscle cramps, and increasingly dark urine. She was found to be anemic, thrombocytopenic, and in acute renal failure. On admission, the direct antiglobulin test was positive for complement (C3) only. After careful review of her medication list, the possibility of DIIHA was raised. She had started taking trimethoprim-sulfamethoxazole (TMP-SMX) for Pneumocystis jiroveci pneumonia prophylaxis 24 days prior on a weekend dose schedule. Serologic tests on peripheral blood samples were performed using standard methods. Drug studies were performed at an immunohematology reference laboratory. RESULTS: The patient's serum showed hemolysis of donor red blood cells in the presence of TMP-SMX and also TMP-SMX-induced platelet antibodies. The patient was treated with transfusions, hemodialysis, and immunosuppressive agents. Her clinical condition improved and she was discharged after 8 days in stable condition. CONCLUSION: This case describes the first reported concurrent DIIHA and DIIT due to TMP-SMX-induced antibodies in an HSCT patient. DIIHA and DIIT can present a diagnostic challenge in the setting of intermittent medication dosing.