Association of acute neurological symptoms with mortality in patients with heat-related illness: a nationwide study in Japan

BACKGROUND AND OBJECTIVE: Heat-related illnesses can range from mild to severe, potentially causing death or disability. Central nervous system abnormalities are crucial clinical indicators, yet their relationships with outcomes remain unclear. We aimed to investigate this association using a Japanese nationwide database. METHODS: This study analysed data from the Heatstroke Study database (2017-2021) which included adult Japanese patients with heat-related illnesses. Acute neurological symptoms (Glasgow Coma Scale (GCS) <14 and/or seizures) were the primary exposure. Outcomes included in-hospital mortality and unfavourable functional outcomes (modified Rankin Scale (mRS) ≥3). Adjusted ORs with 95% CIs were estimated using multivariable logistic regression, adjusting for age, sex, preadmission mRS, Charlson Comorbidity Index, occurrence situation, body temperature and systolic blood pressure. RESULTS: Among 2961 patients (median age 73.0 years, 69.4% were male), the in-hospital mortality was 5.4% (160/2961). The observed mortality was 10.9% (142/1303) in patients with acute neurological symptoms and 1.1% (18/1658) in patients without symptoms. Unfavourable functional outcomes occurred in 42.2% (455/1078) of patients with acute neurological symptoms and 10.4% (155/1492) of patients without symptoms. After adjustment, acute neurological symptoms were found to be significantly associated with in-hospital mortality (adjusted OR 7.33, 95% CI 4.50 to 12.64) and unfavourable functional outcomes (adjusted OR 5.15, 95% CI 4.14 to 6.44). A dose-dependent relationship was observed between GCS severity and mortality, with GCS 3-8 showing the highest risk compared with GCS 14-15 (adjusted OR 12.23, 95% CI 7.42 to 21.17). CONCLUSION: Acute neurological symptoms, particularly impaired consciousness, were independently associated with mortality and unfavourable outcomes in heat-related illnesses. These findings emphasise the importance of neurological symptoms in severity classification for heat-related illnesses.