Correlations between experienced fatigue, physiological fatigue and motor unit function in patients with demyelinating peripheral nerve disorders

Abstract

Fatigue is a common complaint in patients with neurological disorders. Fatigue is well documented in disorders of the central nervous system such as multiple sclerosis and post-stroke. Although acknowledged, fatigue in disorders of the peripheral nervous system is less studied and underlying pathophysiology is not understood. It has been hypothesised that fatigue may relate to progressive loss of peripheral motor units or disorganised peripheral motor unit firing. This study aimed to explore experienced fatigue in chronic demyelinating disorders of the peripheral nerves and relationship with quality of life. The study also aimed to investigate peripheral motor unit function using a newly-developed electrophysiology technique, explore how this relates to self-reported experience of fatigue and development of muscle fatigue during exertion. Fatigue in patients with chronic demyelinating disorders of the peripheral nervous system appears to be negatively correlated with quality of life. Patients with both acquired and hereditary chronic demyelinating peripheral nerve disorders have reduced number of motor units assessed using MUNIX technique compared to control subjects. However, no clear relationship is found between number of functioning peripheral motor units and fatigue levels experienced by patients. Depression and reduced grip strength were significant predictors of higher experienced fatigue levels in patients with chronic inflammatory demyelinating polyneuropathy. This suggests fatigue in this patient group is likely to be multifactorial, with physical and psychological contributors. Significant changes in MUNIX values were found following intravenous immunoglobulin therapy in patients with chronic inflammatory demyelinating polyneuropathy, highlighting a potential role as a monitoring tool for treatment response.