On the morning before admission, the patient received C6D17 of maintenance carfilzomib, which had been delayed from day 15 because of the holiday. Later that evening, he developed nausea, vomiting, and fever of 101.3 °F. He presented to the VA emergency department and was tachycardic (108 beats per minute) and hypotensive (86/55 mm Hg). Laboratory tests were notable for hemoglobin level 9.9 g/dL (prior 11.6 g/dL), platelet count 270 K/µL, and creatinine level 1.86 mg/dL (prior 1.12 mg/dL). A respiratory viral panel was positive for influenza A, and antimicrobial agents were eventually broadened to piperacillin-tazobactam, azithromycin, and oseltamivir. His outpatient medications, which included acyclovir, zoledronic acid, sulfamethoxazole/trimethoprim, aspirin, amlodipine, atorvastatin, omeprazole, zolpidem, calcium, vitamin D, loratadine, ascorbic acid, and prochlorperazine, were continued as indicated.
On hospital day 2, the patient’s platelet count declined from 211 to 57 K/µL. He developed tea-colored urine (UA 2+ blood, 0-2 RBC/HPF) and had laboratory tests suggestive of hemolysis, including LDH 910 IU/L (reference range, 60-250 IU/L), total bilirubin 3.3 mg/dL (reference range, 0.2-1.3 mg/dL; no direct or indirect available), and a peripheral blood smear demonstrating moderate microangiopathy. Although haptoglobin level was normal at this time (206 mg/dL; reference range, 44-215 mg/dL), it decreased to 42 mg/dL by the following day. Additional workup included a negative direct Coombs and a DIC panel showing elevated fibrinogen (596 mg/dL; reference range, 200-400 mg/dL) and mildly elevated INR (1.16). Blood cultures remained negative, and a 22-pathogen GI PCR panel identified no viral or bacterial pathogens, including E coli O157:H7. C3 (114 mg/dL; reference range, 90-180 mg/dL) and C4 (40 mg/dL; reference range, 16-47 mg/dL) complement levels were both normal.
Based on these findings, empiric treatment was started with plasma exchange and pulse-dosed steroids. The patient received 3 cycles of plasma exchange until the results of the ADAMTS13 activity ruled out TTP (63% enzyme activity). Over the next 6 days, his platelet count reached a nadir of 6 K/µL and creatinine level peaked at 10.36 mg/dL, necessitating the initiation of hemodialysis. Given severe renal insufficiency, a diagnosis of atypical HUS was again considered, and eculizumab 900 mg was administered on days 9 and 16 with stabilization of renal function. By the time of discharge on day 17, the patient’s creatinine level had decreased to 4.17 mg/dL and platelet count was 164 K/µL. Creatinine level normalized to 1.02 mg/dL by day 72.
Outpatient genetic testing through the BloodCenter of Wisconsin Diagnostic Laboratories was negative for gene mutations associated with atypical HUS. Approximately 1 month after discharge, the patient resumed maintenance lenalidomide alone without reinitiation of proteasome inhibitor therapy.
Discussion
In this case series, we describe the uncommon drug-related adverse event of TMA occurring in 2 patients with MM after receiving carfilzomib. Although the incidence of TMA disorders is low, reaching up to 2.8% in patients receiving carfilzomib plus cyclophosphamide and dexamethasone in the phase 2 CARDAMON trial, our experience suggests that a high index of suspicion for carfilzomib-induced TMA is warranted in the real-world setting.8 TMA syndromes, including TTP, HUS, and DITMA, are characterized by microvascular endothelial injury and thrombosis leading to thrombocytopenia and microangiopathic hemolytic anemia.5,9 Several drug culprits of DITMA are recognized, including quinine, gemcitabine, tacrolimus, and proteasome inhibitors (bortezomib, carfilzomib, ixazomib).10-12 In a real-world series of patients receiving proteasome inhibitor therapy, either carfilzomib (n=8) or bortezomib (n=3), common clinical features of DITMA included thrombocytopenia, microangiopathic hemolytic anemia, gastrointestinal symptoms, and renal insufficiency with or without a need for hemodialysis.2 Although DITMA has been described primarily as an early event, its occurrence after 12 months of proteasome inhibitor therapy has also been reported, both in this series and elsewhere, thereby suggesting an ongoing risk for DITMA throughout the duration of carfilzomib treatment.2,13
