Myalgic Encephalomyelitis, Chronic Fatigue Syndrome, and Systemic Exertion Intolerance Disease: Three Distinct Clinical Entities

Frank Twisk

doi:10.3390/challe9010019

Abstract

Many researchers consider chronic fatigue syndrome (CFS) to be a synonym of Myalgic Encephalomyelitis (ME). However, the case criteria of ME and CFS define two distinct clinical entities. Although some patients will meet both case criteria, other patients can meet the diagnosis of ME and not fulfil the case criteria for CFS, while the diagnosis of CFS is largely insufficient to be qualified as a ME patient. ME is a neuromuscular disease with distinctive muscular symptoms, including prolonged muscle weakness after exertion, and neurological signs implicating cerebral dysfunction, including cognitive impairment and sensory symptoms. The only mandatory symptom of CFS is chronic fatigue. Chronic fatigue must be accompanied by at least four out of eight nonspecific symptoms: substantial impairment in short-term memory or concentration, a sore throat, tender lymph nodes, muscle pain, multijoint pain, a new type of headaches, unrefreshing sleep, and postexertional “malaise” lasting more than 24 h. So, regardless whether the name ME is appropriate or not, ME is not synonymous to CFS. That is not a matter of opinion, but a matter of definition. Due to the definitions of ME and CFS, “ME/CFS” does not exist and cannot be replaced by a new clinical entity (SEID: Systemic Exertion Intolerance Disease), as recently suggested.

Highlights

Many researchers consider Myalgic Encephalomyelitis (ME) [1] and chronic fatigue syndrome (CFS) [2] to be “conditions with similar symptoms” [3].considering the case criteria defining the clinical entities, this position is incorrect.While ME [1] is defined as a “polio-like” neuromuscular disease with distinctive features, CFS [2]is a heterogeneous condition characterized by chronic fatigue, accompanied by four out of eight “additional symptoms”
ME has been described in the medical literature under various names, including “atypical poliomyelitis” and “epidemic neuromyasthenia” since 1936 [4], often on account of outbreaks [5,6,7]
ME has been classified as a neurological disease by the World Health Organization

Summary

Introduction

Many researchers consider ME [1] and CFS [2] to be “conditions with similar symptoms” [3]. SEID [3], suggested to replace ME and CFS in the future, is defined by fatigue, postexertional “malaise”, unrefreshing sleep, and at least one of two other symptoms. According to the case criteria for CFS from 1994 [2], most commonly used in CFS research in the last decades, “persistent or relapsing chronic fatigue” (lasting more than six months) must be accompanied by at least four out of eight symptoms: impaired memory or concentration, sore throat, tender cervical or axillary lymph nodes, muscle pain, multijoint pain, new headaches, unrefreshing sleep, and postexertional “malaise”. Chronic fatigue (mandatory) and at least four of the following eight symptoms: Substantial impairment in short-term memory or concentration, a sore throat, tender lymph nodes, muscle pain, multijoint pain, headaches (of a new type, pattern, or severity), unrefreshing sleep, and postexertional “malaise”. Chronic fatigue (not lifelong, not due to ongoing excessive exertion, and not alleviated by rest), postexertional “malaise”, unrefreshing sleep, and cognitive impairment and/or orthostatic intolerance

Diagnosis

Conclusions