(Mentions HMSN/CMT) Clinical Neurophysiology of Fatigue

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Clinical Neurophysiology of Fatigue

by MJ Zwarts, et al.

http://www.immunesupport.com/library/showarticle.cfm/ID/8601

Fatigue is a multidimensional concept covering both physiological

and psychological aspects. Chronic fatigue is a typical symptom of

diseases such as cancer, multiple sclerosis (MS), Parkinson's

disease (PD) and cerebrovascular disorders but is also presented by

people in whom no defined somatic disease has been established. If

certain criteria are met, Chronic Fatigue Syndrome can be diagnosed.

The 4-item Abbreviated Fatigue Questionnaire allows the extent of

the experienced fatigue to be assessed with a high degree of

reliability and validity. Physiological fatigue has been well

defined and originates in both the peripheral and central nervous

system. The condition can be assessed by combining force and surface-

EMG measurements (including frequency analyses and muscle-fibre

conduction estimations), twitch interpolation, magnetic stimulation

of the motor cortex and analysis of changes in the readiness

potential.

Fatigue is a well-known phenomenon in both central and peripheral

neurological disorders. Examples of the former conditions are

multiple sclerosis, Parkinson's disease and stroke. Although it

seems to be a universal symptom of many brain disorders, the unique

characteristics of the concomitant fatigue also point to a specific

relationship with several of these syndromes.

As regards neuromuscular disorders, fatigue has been reported in

patients with post-polio syndrome, myasthenia gravis, Guillain-Barré

syndrome, facioscapulohumeral dystrophy, myotonic dystrophy and

hereditary motor and sensory neuropathy type-I. More than 60% of all

neuromuscular patients suffer from severe fatigue, a prevalence

resembling that of patients with MS.

Except for several rare myopathies with specific metabolic

derangements leading to exercise-induced muscle fatigue, most

studies have not identified a prominent peripheral cause for the

fatigue in this population. In contrast, the central activation of

the diseased neuromuscular system is generally found to be

suboptimal. The reliability of the psychological and clinical

neurophysiological assessment techniques available today allows a

multidisciplinary approach to fatigue in neurological patients,

which may contribute to the elucidation of the pathophysiological

mechanisms of chronic fatigue, with the ultimate goal to develop

tailored treatments for fatigue in neurological patients.

The present report discusses the different manifestations of fatigue

and the available tools to assess peripheral and central fatigue.