Short-Term Biceps Muscle Wasting Assessed by Serial Ultrasound as a Predictor of Survival Duration in Terminally Ill Cancer Patients: A Retrospective Cohort Study

<i>Background and Objectives:</i> Rapid physiological decline in terminal cancer is frequently accompanied by accelerated skeletal muscle loss. Although bedside ultrasonography (US) is practical and feasible in palliative care settings, the prognostic relevance of short-term muscle change remains unclear. This study aimed to evaluate whether the rate of muscle loss over a 10-day period, assessed by serial ultrasound, is associated with survival duration in terminally ill cancer patients. <i>Materials and Methods:</i> This single-center retrospective cohort study included 87 inpatients with end-stage cancer who underwent bedside ultrasound measurements of the biceps brachii (BB) and rectus femoris (RF). Baseline US was performed within the first three days of admission, followed by a repeat assessment 10 days after baseline (day-10 follow-up ultrasound). Muscle thickness (MT) measurements were normalized by height squared (m²), and 10-day changes were calculated as delta (Δ) indices, defined as baseline minus day-10 values. Because the exposure of interest (Δ) can only be determined after completion of the day-10 assessment, survival timing analyses were anchored to this prespecified landmark. Survival duration was defined as the number of days from the day-10 follow-up ultrasound to death among patients who died within one year. Associations between muscle changes and survival duration were evaluated using correlation analyses and multivariable linear regression adjusted for age, sex, body mass index, Eastern Cooperative Oncology Group (ECOG) performance status, and nutritional risk. The primary analyses focused on survival timing among decedents. <i>Results:</i> Significant muscle loss was observed over the 10-day interval between baseline and 10 days after baseline. Among the 58 patients who died within one year, greater short-term biceps muscle loss, reflected by higher Δ BB muscle thickness index (Δ BB MT-I), was moderately associated with shorter survival duration (r = -0.437, <i>p</i> = 0.0006). In multivariable linear regression analysis, Δ BB MT-I remained independently associated with survival duration (β = -701.19; 95% CI: -1102 to -301; <i>p</i> = 0.0006), whereas RF muscle changes and baseline clinical variables were not statistically significant. <i>Conclusions:</i> Short-term biceps muscle loss assessed by serial ultrasound, as reflected by Δ BB MT-I, is associated with shorter survival duration in terminally ill cancer patients. These findings suggest that dynamic muscle changes, rather than single-time-point measurements, may provide clinically meaningful insight into short-term survival timing. Serial bedside muscle ultrasound may serve as a low-burden adjunct for prognostic communication in palliative care, although prospective time-to-event studies are required for validation.