Idiopathic chronic fatigue and myalgia syndrome (myalgic encephalomyelitis): some thoughts on nomenclature and aetiology

The aetiopathogenesis of fatigue: unpredictable, complex and persistent

BACKGROUND

Chronic fatigue syndrome is a common condition characterized by severe fatigue with post-exertional malaise, impaired cognitive ability, poor sleep quality, muscle pain, multi-joint pain, tender lymph nodes, sore throat or headache. Its defining symptom, fatigue is common to several diseases.

AREAS OF AGREEMENT

Research has established a broad picture of impairment across autonomic, endocrine and inflammatory systems though progress seems to have reached an impasse.

AREAS OF CONTROVERSY

The absence of a clear consensus view of the pathophysiology of fatigue suggests the need to switch from a focus on abnormalities in one system to an experimental and clinical approach which integrates findings across multiple systems and their constituent parts and to consider multiple environmental factors.

GROWING POINTS

We discuss this with reference to three key factors, non-determinism, non-reductionism and self-organization and suggest that an approach based on these principles may afford a coherent explanatory framework for much of the observed phenomena in fatigue and offers promising avenues for future research.

AREAS TIMELY FOR DEVELOPING RESEARCH

By adopting this approach, the field can examine issues regarding aetiopathogenesis and treatment, with relevance for future research and clinical practice.

Inflammatory fatigue and sickness behaviour - lessons for the diagnosis and management of chronic fatigue syndrome

Persistent and severe fatigue is a common part of the presentation of a diverse range of disease processes. There is a growing body of evidence indicating a common inflammatory pathophysiology underlying many conditions where fatigue is a primary patient concern, including chronic fatigue syndrome. This review explores current models of how inflammatory mediators act on the central nervous system to produce fatigue and sickness behaviour, and the commonality of these processes in conditions as diverse as surgical trauma, infection, various cancers, inflammatory bowel disease, connective tissue diseases and autoimmune diseases. We also discuss evidence indicating chronic fatigue syndrome may have important pathophysiological similarities with cytokine mediated sickness behaviour, and what lessons can be applied from sickness behaviour to chronic fatigue syndrome with regards to the diagnosis and management.

Chronic fatigue syndrome

During the past two decades, there has been heated debate about chronic fatigue syndrome (CFS) among researchers, practitioners, and patients. Few illnesses have been discussed so extensively. The existence of the disorder has been questioned, its underlying pathophysiology debated, and an effective treatment opposed; patients' organisations have participated in scientific discussions. In this review, we look back on several controversies over CFS with respect to its definition, diagnosis, pathophysiology, and treatment. We review issues of epidemiology and clinical manifestations, focusing on the scientific status of CFS. Modern neuroscience and genetics research offer interesting findings for new hypotheses on the aetiology and pathogenesis of the illness. We also discuss promising future issues, such as psychopathophysiology and mechanisms of improvement, and suggest multidisciplinary prospective studies of CFS and fatigue in the general population. These studies should pay particular attention to similarities to and differences from functional somatic syndromes and other fatiguing conditions.

[Definition of "chronic fatigue syndrome" (CFS)]

The definition of "Chronic Fatigue Syndrome" (CFS) in 1988 was an attempt to establish a uniform basis for the previously heterogeneous approaches to research of this severe and inexplicable state of fatigue. At the same time, researchers wished to narrow down a pathogenetically founded disease entity a priori by specifying precise disease criteria. The empirical data gathered in accordance with the CFS definition, however, have failed to confirm the assumption that the disease entity is pathogenetically uniform. Furthermore, the originally selected criteria have proven to be impracticable ore theoretically questionable. In the period that followed, modifications that permitted a more comprehensive and yet more differentiated classification of fatigue states of unclear etiology were proposed. The new research approach avoids postulation of causal entities and puts CFS back in a category with other descriptive states of fatigue.

Psychosocial management of chronic fatigue syndrome in adolescence

The state of chronic fatigue syndrome (CFS) as abnormal illness behaviour or as biologically determined disease is undecided. The ensuing, often public, debate has confused the community and has led to sharp differences in the therapeutic approach to individual patients. These challenges are compounded when the patient is an adolescent and intergenerational issues enter the picture. Two adolescent cases with different outcomes are presented and the principles of a rehabilitation approach to treatment are outlined which attempt to avoid being drawn into unproductive debates about aetiology.

[Chronic fatigue syndrome]

Reports on conditions of chronic fatigue associated with other somatopsychic symptoms after acute viral infections have led to the hypothesis of a "chronic fatigue syndrome" (CFS). Historical disease descriptions, like e.g. "myalgic encephalomyelitits", were updated by means of modern virological diagnostic techniques and data analysis. Several viral agents like enteroviruses, Epstein-Barr virus, Human-Herpesvirus 6 and other herpesviruses have been implicated for possible underlying infections. A preliminary disease definition by the Center for Disease Control (CDC) seeks to provide a rational basis for further etiological studies. In fact, there is growing consensus that the syndrome comprises various separate disease entities and causative agents. Today we can tentatively differentiate a "chronic mononucleosis" after infection with Epstein-Barr virus, an etiologically undetermined "postviral fatigue syndrome" and a fatigue syndrome of the myalgic type after Coxsackie-B virus infection. Furthermore, a valid diagnosis of CFS must be based on the exclusion of defined other diseases and the awareness of dealing with a hypothetical concept. As a result, current knowledge does not yet allow specific therapeutic recommendations.

Fatigue syndromes: a comparison of chronic "postviral" fatigue with neuromuscular and affective disorders

Patients (n = 47) presenting to a neurological centre with unexplained chronic "postviral" fatigue (CFS) were studied prospectively. Controls were patients with peripheral fatiguing neuromuscular diseases and inpatients with major depression in a psychiatric hospital. Seventy-two percent of the CFS patients were cases of psychiatric disorder, using criteria that excluded fatigue as a symptom, compared with 36% of the neuromuscular group. There was no difference in subjective complaints of physical fatigue between all groups. Mental fatigue and fatigability was equally common in CFS and affective patients, but only occurred in those neuromuscular patients who were also cases of psychiatric disorder. Overall, the CFS patients more closely resembled the affective than the neuromuscular patients. Attribution of symptoms to physical rather than psychological causes was the principal difference between matched CFS and psychiatric controls. The symptoms of "postviral" fatigue had little ability to discriminate between CFS and affective disorder. The fatigue in CFS appeared central in origin, suggesting it is not primarily a neuromuscular illness. The implications for research and treatment of chronic fatigue are discussed.