Fatigue in amyotrophic lateral sclerosis/motor neuron disease: prevalence, influences and trajectories

Objective: In a large cohort of people with amyotrophic lateral sclerosis/motor neuron disease (pwALS), we examined the age-sex prevalence of fatigue, its relationship to other symptoms and functioning, and trajectories over time. Methods: Data from the Trajectories of Outcome in Neurological Conditions study were analyzed by Rasch analysis, structural equation and group-based trajectory models. Results: Fatigue was reported by 97.8% on Neurological Fatigue Index-MND (NFI-MND) and 96.4% on Numeric Rating Scale Fatigue among 1058 pwALS: mean age 65 (range 20-90); mean duration 23 months (range 0-301); 60.7% male; onset 26.5% Bulbar, 71.5% Limb and 2.0% Respiratory. Mean (metric) level on NFI-MND was 12.8 (SD 5.3; range 0-24). Cut-points on the NFI-MND of 10 and 15 divided fatigue into mild (27.3%); moderate (36.1%) and severe (36.2%). Structural equation modeling showed that function, cognition, spasticity, dyspnea and pain have descending order of effect. Over average 11.6 months follow-up, 60.5% had stable fatigue, 23.8% increased fatigue level, while 15.8% showed declining fatigue. Trajectory analysis showed three groups, low, average and high fatigue. Those with low trajectories had less spasticity, worry, cognitive problems, as well as better functioning, longer duration and were less likely to be male. High fatigue trajectory was associated with worse spasticity, cognition and anxiety. Conclusions: Fatigue is extremely common among pwALS, thus more work is required on fatigue management. In addition to treating fatigue itself, the current study shows that targeting cognition, spasticity, dyspnea and pain might be fruitful.