Tag: neurophysiology

The role of clinical neurophysiology in the definition and assessment of fatigue and fatigability

Highlights:

  • Though a common symptom, fatigue is difficult to define and investigate, and occurs in a wide variety of disorders, with differing pathological causes.
  • This review aims to guide clinicians in how to approach fatigue and to suggest that neurophysiological tests may allow an understanding of its origin and severity.
  • The effectiveness of neurophysiological tests as cost-effective objective biomarkers for the assessment of fatigue has been summarised.

Abstract

Though a common symptom, fatigue is difficult to define and investigate, occurs in a wide variety of neurological and systemic disorders, with differing pathological causes. It is also often accompanied by a psychological component. As a symptom of long-term COVID-19 it has gained more attention.

In this review, we begin by differentiating fatigue, a perception, from fatigability, quantifiable through biomarkers. Central and peripheral nervous system and muscle disorders associated with these are summarised. We provide a comprehensive and objective framework to help identify potential causes of fatigue and fatigability in a given disease condition. It also considers the effectiveness of neurophysiological tests as objective biomarkers for its assessment. Among these, twitch interpolation, motor cortex stimulation, electroencephalography and magnetencephalography, and readiness potentials will be described for the assessment of central fatigability, and surface and needle electromyography (EMG), single fibre EMG and nerve conduction studies for the assessment of peripheral fatigability.

The purpose of this review is to guide clinicians in how to approach fatigue, and fatigability, and to suggest that neurophysiological tests may allow an understanding of their origin and interactions. In this way, their differing types and origins, and hence their possible differing treatments, may also be defined more clearly.

Source: Tankisi H, Versace V, Kuppuswamy A, Cole J. The role of clinical neurophysiology in the definition and assessment of fatigue and fatigability. Clin Neurophysiol Pract. 2023 Dec 18;9:39-50. doi: 10.1016/j.cnp.2023.12.004. PMID: 38274859; PMCID: PMC10808861. https://www.sciencedirect.com/science/article/pii/S2467981X23000367 (Full text)

Neurophysiology of postviral fatigue syndrome

Abstract:

The exact pathophysiology of excessive fatigue in patients with postviral fatigue syndrome (PVFS) remains uncertain in spite of increasing investigation. One objective abnormality of neuromuscular function is the increased jitter on single fibre EMG studies. While this is a sensitive technique which indicates a disturbance in the peripheral part of the motor unit, it is non-specific and its role in the pathophysiology remains unclear.

Impaired muscular activation with added force in response to superimposed electrical stimulation suggests an extra-muscular and/or central component of fatigue. Conventional neurophysiological studies and those of strength and endurance have shown no objective abnormality in patients compared with controls. The previous reports of disturbed muscle metabolism on NMR spectroscopy have not been confirmed in more recent studies and no consistent abnormality of excitation-contraction coupling has so far emerged.

Finally, unlike patients with depression, cognitive evoked potential studies suggest impaired attention, memory and stimulus evaluation in postviral fatigue syndrome. In future studies, the importance of utilising approved clinical criteria for patient inclusion cannot be overemphasized. Control groups should include sedentary or deconditioned as well as depressed subjects to help standardise these important variables.

 

Source: Jamal GA, Miller RG. Neurophysiology of postviral fatigue syndrome. Br Med Bull. 1991 Oct;47(4):815-25. http://www.ncbi.nlm.nih.gov/pubmed/1794086