Functional trajectories beyond 90 days after endovascular thrombectomy: a systematic review with primary synthesis and supportive narrative evidence.

Background: The modified Rankin Scale (mRS) score at 90 days is the conventional functional endpoint in studies of endovascular thrombectomy (EVT). However, it remains uncertain whether functional status after EVT is truly stable by 90 days. Although an increasing number of studies report outcomes at 1 year or later, only a small proportion directly examine within-patient functional change beyond the conventional 90-day time point. Methods: We performed a systematic review of functional trajectories beyond 90 days after EVT. PubMed, Embase, Web of Science, and the Cochrane Library were searched. Studies were screened using a hierarchical framework to distinguish directly eligible post-90-day trajectory studies from studies providing broader supportive evidence on long-term outcome. Because the directly eligible literature was limited and heterogeneous with respect to study population, follow-up structure, denominator definition, and transition operationalization, we conducted a structured primary synthesis rather than a conventional pooled meta-analysis. Results: A total of 283 records were identified, of which 52 full-text reports were assessed for eligibility. Fourteen studies were retained in the final review; however, only 3 studies directly examined within-patient functional transition beyond the conventional 90-day endpoint and were included in the primary synthesis, whereas 11 studies were retained as supportive or discussion-only evidence. The directly eligible studies showed that functional outcome after EVT is not invariably fixed at 90 days. Two studies identified delayed functional improvement beyond the conventional endpoint, whereas one multicenter study showed that late functional deterioration between 90 days and 1 year occurred in 21.5% of patients with vertebrobasilar artery occlusion. Taken together, the directly eligible evidence suggests that post-90-day functional outcome after EVT may be bidirectional, with both later recovery and later decline observed. Conclusion: Current evidence suggests that 90-day outcome after EVT may not always represent final recovery. Both delayed functional improvement and late functional deterioration appear possible beyond the conventional short-term endpoint, but the certainty of current evidence remains low. These findings should therefore be regarded as hypothesis-generating and support the need for prospective, standardized, trajectory-based follow-up after EVT.