Muscle loss must be interpreted in the context of fluid imbalance: a dual-parameter model predicts functional outcomes after acute stroke

Kota Amakasu; Tatsuro Inoue; Araki Saito; Natsumi Kamada; Akiko Brown; Akari Kasai; Mei Furusawa; Sota Kobayashi; Yumiko Watanabe

doi:10.1007/s41999-026-01464-4

Muscle loss must be interpreted in the context of fluid imbalance: a dual-parameter model predicts functional outcomes after acute stroke

Eur Geriatr Med. 2026 Apr 5. doi: 10.1007/s41999-026-01464-4. Online ahead of print.

Authors

Kota Amakasu^{1

2}, Tatsuro Inoue³, Araki Saito^{2

4}, Natsumi Kamada^{2

5}, Akiko Brown^{2

6}, Akari Kasai², Mei Furusawa², Sota Kobayashi², Yumiko Watanabe¹

Affiliations

¹ Department of Rehabilitation, Shinrakuen Hospital, Niigata, Japan.
² Graduate School of Health and Welfare, Niigata University of Health and Welfare, 1398, Shimami-cho, Kita-ku, Niigata-shi, Niigata-ken, 950-3198, Japan.
³ Graduate School of Health and Welfare, Niigata University of Health and Welfare, 1398, Shimami-cho, Kita-ku, Niigata-shi, Niigata-ken, 950-3198, Japan. tatsuro-inoue@nuhw.ac.jp.
⁴ Department of Nutrition, Yoshida Hospital, Niigata, Japan.
⁵ Department of Rehabilitation, Nippon Medical School Chiba Hokusoh Hospital, Chiba, Japan.
⁶ Department of Nutrition, Kitanakagusuku wakamatsu Hospital, Okinawa, Japan.

PMID: 41936000
DOI: 10.1007/s41999-026-01464-4

Abstract

Aim: To examine whether the coexistence of elevated extracellular water-to-total body water ratio (ECW/TBW) and low appendicular lean soft tissue index (ALSTI), a combined fluid-muscle phenotype, predicted poorer functional independence at hospital discharge.

Findings: The coexistence of high ECW/TBW and low ALSTI was associated with poorer functional independence at hospital discharge, whereas low ALSTI alone was not.

Message: The interpretation of ALSTI in patients with acute stroke should consider ECW/TBW and that ALSTI with ECW/TBW is clinically useful in predicting prognosis.

Purpose: We aimed to examine whether the coexistence of elevated extracellular water-to-total body water ratio (ECW/TBW) and low appendicular lean soft tissue index (ALSTI), a combined fluid-muscle phenotype, predicted poorer functional independence at hospital discharge.

Methods: Patients aged ≥65 years with an acute stroke between 2021 and 2024 were included. Baseline body composition was measured using bioelectrical impedance analysis within one week of rehabilitation initiation. High ECW/TBW was defined as ≥0.400, and low ALSTI as <7.0 kg/m² for males and <5.7 kg/m² for females. Functional independence at discharge was assessed using the modified Rankin Scale (mRS), with scores of 0-2 defined as independent and 3-6 defined as non-independent. Multivariate logistic regression analysis was used to examine the effects of the coexistence of high ECW/TBW and low ALSTI on functional independence.

Results: In total, 560 patients were included in the analysis. The number of patients with high ECW/TBW and low ALSTI was 227 (49.4%). Multivariate logistic regression analysis showed that the coexistence of high ECW/TBW and low ALSTI at baseline was a significant associated with non-independence at discharge (odds ratio (OR) = 3.82, 95% confidence interval (CI) 2.00-7.32, P < 0.001), but low ALSTI alone was not (OR = 1.73, 95% CI 0.92-3.22, P = 0.086).

Conclusions: Baseline coexistence of high ECW/TBW and low ALSTI, highlighting the importance of considering fluid imbalance in addition to muscle mass, was associated with for non-independence at hospital discharge in patients with acute stroke.

Keywords: Acute rehabilitation; Body composition; Cerebrovascular disorder; Fluid balance; Functional status; Muscular atrophy.