Clinical neurophysiology of fatigue

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Clin Neurophysiol. 2007 Nov 24

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; Neuromuscular Centre Nijmegen, Department

of Neurology, Radboud University Nijmegen Medical Centre, 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.