Clinical neurophysiology of fatigue

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Clin Neurophysiol. 2008 Jan;119(1):2-10.

Clinical neurophysiology of fatigue.

Zwarts MJ, Bleijenberg G, van Engelen BG.

University Medical Centre Nijmegen, Institute of Neurology, 920

Department of Clinical Neurophysiology, PO Box 9101, 6500 HB

Nijmegen, The Netherlands.

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-Barre

syndrome, facioscapulohumeral dystrophy, myotonic dystrophy and

Hereditary Motor and Sensory Neuropathy type-I.(CMT) 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.