Salivary Dim‐Light Melatonin Onset is Associated with Functional Decline, Respiratory Symptom Emergence, and Survival in Early Amyotrophic Lateral Sclerosis

OBJECTIVE: Sleep-wake and circadian disturbances are increasingly recognized in people living with amyotrophic lateral sclerosis (plwALS), but endogenous circadian phase timing and its prognostic significance in early disease remain unclear. We assessed whether salivary dim-light melatonin onset (DLMO), an objective marker of central circadian phase, is altered in early plwALS and whether it provides prognostic information. METHODS: In this prospective longitudinal observational study, plwALS within 18 months of symptom onset underwent home-based salivary melatonin sampling under dim-light conditions at 6 predefined time points around habitual sleep onset. Melatonin profiles were modeled using cubic smoothing splines, and DLMO was defined when the fitted curve first reached 3 pg/ml. Clinical, respiratory, and sleep assessments were collected at baseline (T0) and after 6 months (T6); a subgroup repeated saliva sampling at T6. Age- and sex-matched controls underwent melatonin profiling. Associations with disease progression, incident respiratory symptoms, and survival/tracheostomy were examined using regressions and survival analyses. RESULTS: A total of 50 plwALS were enrolled. Compared with controls, plwALS showed an earlier DLMO (20:24 ± 1:18 vs 20:58 ± 0:50; p = 0.028) despite similar habitual sleep onset and chronotype. Within ALS cohort, a later baseline DLMO correlated with worse functional/motor status, faster progression of disease, incident dyspnea/orthopnea by T6 (adjusted OR 3.11; p = 0.019), and poorer survival/tracheostomy-free outcome. In the resampled subgroup (n = 28), DLMO and melatonin-derived metrics did not change over ~6 months. INTERPRETATION: Circadian phase alterations are detectable in early ALS. Baseline DLMO showed exploratory associations with functional, respiratory, and survival outcomes. Larger independent cohorts are required before DLMO can be considered a validated prognostic biomarker. ANN NEUROL 2026.