Hyponatremia in the Prognosis of Acute Ischemic Stroke

Background: Hyponatremia is a risk factor for stroke and cardiovascular disease. Even mild hyponatremia is associated with increased 30-day mortality after myocardial infarction, and it has recently shown to increase the 3-year mortality after a stroke. In this work, we investigated both acute and chronic clinical outcomes after a stroke in hyponatremic patients. Methods: We reviewed all patients admitted between 2004 and 2011 with the diagnosis of acute ischemic stroke. Hyponatremia was defined as serum sodium level less than 135 mmol/L and recorded on admission. All hemorrhagic strokes were excluded. Data were analyzed using multivariate logistic regression. Results: A total of 3585 patients with stroke were identified. Hyponatremia was observed in 565 (16%) patients. Baseline characteristics were similar between groups except heart failure (P - .015), cancer (P - .038), diabetes (P < .001), and dementia (P = .015). Hyponatremic patients had higher National Institutes of Health Stroke Scale (NIHSS) score on admission (P = .032) and at discharge (P = .02). Despite similar modified Barthel Index (mBI) preadmission, patients with hyponatremia had worse mBI on admission (P - .049). Hyponatremia was associated with higher mortality in hospital (P = .039) and at 3-month (P = .001) and 12-month follow-ups (P = .001). A poorer discharge disposition was seen in the hyponatremia group (P = .004). Complications during admission were similar between groups except for urinary infection (P = .008). Patients with hyponatremia had worse NIHSS and mBI values on admission, and their deficits worsened during their hospitalization. Conclusions: This is the first study to demonstrate that hyponatremia is associated with acute mortality and poorer discharge dispositions and to confirm that higher mortality occurs in these patients, even after 12 months after a stroke.