Seasonal variations in outcomes following spontaneous intracerebral hemorrhage: a case control study

While seasonal variations in the incidence of spontaneous intracerebral hemorrhage (ICH) are well-recognized, the impact of onset season on outcomes remains poorly defined. This study investigated the association between the season of onset and outcomes in ICH patients. We retrospectively analyzed 363 consecutive ICH patients between May 2018 and May 2020 in the First Affiliated Hospital of Wenzhou Medical University. The primary outcome was poor 90-day functional recovery modified Rankin Scale (mRS) 4–6. Secondary outcomes included 90-day Barthel Index (BI) ≤ 60, prolonged length of stay (LOS), and hematoma expansion (HE). Univariate and multivariate logistic regression models were used to assess the relationship between onset season and outcomes. Subgroup analyses further evaluated the robustness of these findings. Of the 363 patients included, 115 (31.7%) presented in spring, 54 (14.9%) in summer, 95 (26.2%) in autumn, and 99 (27.3%) in winter. Compared with winter, autumn onset was independently associated with a significantly lower risk of poor 90-day functional outcome (aOR1: 0.352, 95% CI: 0.186–0.666; aOR2: 0.394, 95% CI: 0.203–0.763). This protective effect remained consistent across subgroups, particularly in males, patients aged < 70 years, and those with a GCS score ≥ 5. In the GCS ≥ 5 subgroup, summer onset was associated with a lower risk of 90-day mRS 4–6 and BI ≤ 60. Autumn onset correlated with reduced risks of both BI ≤ 60 and HE, while spring onset was protective against HE. Additionally, winter onset was linked to the longest LOS. Winter onset was associated with the poorest functional outcomes and prolonged hospitalization. Conversely, autumn and summer onsets were protective against disability, while autumn and spring onsets were linked to a reduced risk of hematoma expansion. Further large-scale prospective validation is required to confirm these seasonal trends in ICH outcomes. The study has been registered at the Chinese Clinical Trial Registry (www.chictr.org.cn), number ChiCTR2200064360, registration date: October 4, 2022.