Dyspnea as a Fatigue-Promoting Factor in ALS and the Role of Objective Indicators of Respiratory Impairment

Context There is no evidence-based treatment for fatigue in amyotrophic lateral sclerosis (ALS), and identification of treatable causes determines management strategies. Although dyspnea is a key symptom of ALS and effectively treatable, it has not been sufficiently investigated whether dyspnea may be a fatigue-promoting factor. Objectives To determine the level of fatigue in dyspneic ALS patients and whether fatigue is promoted by dyspnea. We further evaluated the correlation of fatigue with respiratory function tests. Methods About 101 dyspneic patients and 20 matched controls completed the ALS Functional Rating Scale—Extension and the Fatigue Severity Scale. Dyspneic patients additionally completed the Dyspnea-ALS Scale and the ALS Assessment Questionnaire and underwent respiratory function tests (forced vital capacity, sniff nasal inspiratory pressure, mean inspiratory and expiratory pressure with respective relaxation rates, and blood gases). Multiple regression and correlation analyses were conducted. Results Dyspneic patients had significantly higher fatigue scores than nondyspneic patients, and their fatigue significantly affected quality of life. Dyspnea alone explained up to 24% of the variance in fatigue. No associations were observed between fatigue and respiratory function tests. Patients with noninvasive ventilation reported significantly more dyspnea and fatigue. Conclusion Fatigue is a frequent and bothersome symptom in dyspneic ALS patients. Dyspnea-related distress is, in contrast to objective indicators of respiratory impairment, a determining factor of experienced fatigue. There is an urgent need for further symptom relief beyond noninvasive ventilation. Adequate treatment of dyspnea has the potential for synergies in symptom management arising from the association between fatigue and dyspnea.