Association Between Hyponatremia and Rehabilitation Outcomes After Stroke: A Single-Center Retrospective Cohort Study

Background/Objectives: This study evaluated the association of hyponatremia with functional outcomes and hospital stay length in patients undergoing acute stroke rehabilitation. Methods: We retrospectively reviewed patients undergoing acute stroke rehabilitation. Hyponatremia was identified based on serum sodium levels during hospitalization. After 1:1 propensity score matching (PSM) for age and sex, functional outcomes (Functional Ambulatory Category [FAC], Korean version of the Modified Barthel Index [K-MBI]) and hospital stay were compared between the two groups. Multivariable logistic regression, adjusted for initial NIHSS and baseline FAC/K-MBI scores, was performed to evaluate the independent association of hyponatremia. Results: A total of 141 patients with stroke were analyzed. After 1:1 PSM, 50 patients were included in each group. After matching, the hyponatremia group had higher baseline NIHSS and poorer functional status than the non-hyponatremia group. The hyponatremia group also had significantly longer hospital stays (52.70 ± 24.31 vs. 40.92 ± 17.48 days; p = 0.007) and lower rates of independent ambulation (16% vs. 44%; p = 0.002) and good functional outcomes (22% vs. 56%; p < 0.001). After adjusting for baseline NIHSS and functional status, hyponatremia remained independently associated with lower likelihoods of achieving independent ambulation (adjusted OR [aOR], 0.249; 95% CI, 0.064–0.966; p = 0.044) and good functional outcomes (aOR, 0.283; 95% CI, 0.086–0.929; p = 0.037). Conclusions: Hyponatremia was associated with a lower likelihood of achieving independent ambulation and good functional outcomes after rehabilitation, and with a longer hospital stay in patients with acute stroke.