N-Acetylcysteine Therapy in Thrombotic Thrombocytopenic Purpura: A Systematic Review and Critical Appraisal

Background: Thrombotic thrombocytopenic purpura (TTP) is a life-threatening condition resulting from a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13) deficiency, leading to the accumulation of ultra-large von Willebrand factor (vWF) multimers and widespread microvascular thrombosis. While therapeutic plasma exchange and immunosuppression have significantly improved response, refractory and relapsed disease are significant challenges. N-acetylcysteine (NAC) has emerged as a biologically plausible adjunctive therapy due to its potential to reduce disulfide bonds in vWF multimers. However, its clinical role is unclear. This systematic review aimed to evaluate the clinical evidence regarding the efficacy and safety of N-acetylcysteine in patients with immune-mediated TTP. Methods: We performed a systematic review in accordance with the PRISMA guidelines. PubMed/MEDLINE, Google Scholar, and ClinicalTrials.gov were searched until January 2026. Studies involving patients with immune-mediated TTP treated with NAC were included. Case reports, case series, and observational studies involving patients with immune-mediated TTP treated with NAC were included. Risk of bias was evaluated using adapted quality assessment tools. Results: Sixteen studies encompassing 69 patients met the inclusion criteria. Most reports were case reports or small case series; two were larger observational cohorts. NAC was predominantly used as adjunctive therapy in relapsed or refractory TTP. Dose regimens varied. Platelet recovery following NAC was reported within 1–15 days in responding cases. Predominantly positive haematological responses were observed in small series. Significant heterogeneity in patient populations, timing of initiation, concomitant therapies, and outcome reporting limited causal inference. Conclusions: The current evidence suggests that NAC has a biologically rational and potentially adjunctive value in TTP, particularly in refractory disease or resource-constrained settings. However, current data are largely heterogeneous and derived from low-level evidence. Well-designed prospective studies and randomized controlled trials are needed to determine whether NAC provides significant clinical benefit beyond standard therapy.