Persistent high levels of perceived fatigue are not associated with hypermetabolism in patients with amyotrophic lateral sclerosis

<i>Objective</i>: Fatigue is a common symptom in amyotrophic lateral sclerosis (ALS). Little is known about factors that contribute to fatigue, and whether levels of fatigue change throughout disease course. We aimed to determine associations between self-reported perceived fatigue and metabolic and clinical features of ALS, and perceived fatigue over the course of disease. <i>Methods</i>: This prospective study was conducted between July 2017 and March 2024. Baseline measures of self-reported perceived fatigue, metabolic rate, and clinical measures of disease were assessed in 117 participants with clinically definite or probable ALS. For comparison, fatigue and metabolic rate were collected from 107 control participants. Perceived fatigue was determined using the Fatigue Severity Scale (FSS). Metabolic rate was assessed using indirect calorimetry. Functional capacity and clinical progression were assessed using the ALS Functional Rating Scale-Revised (ALSFRS-R). <i>Results</i>: Baseline levels of perceived fatigue were greater in people living with ALS (plwALS) when compared to controls (5.44 vs. 2.55; <i>p</i> < 0.01). Perceived fatigue was higher in plwALS with lower ALSFRS-R scores and was not associated with measures of metabolism. For most plwALS, perceived fatigue remained high as functional capacity worsened. <i>Conclusion</i>: Our findings confirm higher prevalence of perceived fatigue in plwALS, with persistently high FSS scores reported by most patients during follow-up. High levels of fatigue were not associated with hypermetabolism, suggesting that metabolic rate is unlikely to be a primary contributor. Results highlight a need for further research to identify factors that contribute to fatigue in ALS, and options for improved fatigue management.