Myalgic Encephalomyelitis or What? The International Consensus Criteria.

Abstract

Myalgic encephalomyelitis (ME) is a neuromuscular disease with two distinctive types of symptoms (muscle fatigability or prolonged muscle weakness after minor  exertion and symptoms related to neurological disturbance, especially of sensory,  cognitive, and autonomic functions) and variable involvement of other bodily  systems. Chronic fatigue syndrome (CFS), introduced in 1988 and re-specified in  1994, is defined as (unexplained) chronic fatigue accompanied by at least four  out of eight listed (ill-defined) symptoms. Although ME and CFS are two distinct  clinical entities (with partial overlap), CFS overshadowed ME for decades. In  2011, a panel of experts recommended abandoning the label CFS and its definition  and proposed a new definition of ME: the International Consensus Criteria for ME  (ME-ICC). In addition to post-exertional neuroimmune exhaustion (PENE), a  mandatory feature, a patient must experience at least three symptoms related to  neurological impairments; at least three symptoms related to immune,  gastro-intestinal, and genitourinary impairments; and at least one symptom  related to energy production or transportation impairments to meet the diagnosis  of ME-ICC. A comparison between the original definition of ME and the ME-ICC  shows that there are some crucial differences between ME and ME-ICC. Muscle  fatigability, or long-lasting post-exertional muscle weakness, is the hallmark  feature of ME, while this symptom is facultative for the diagnosis under the  ME-ICC. PENE, an abstract notion that is very different from post-exertional  muscle weakness, is the hallmark feature of the ME-ICC but is not required for  the diagnosis of ME. The diagnosis of ME requires only two type of symptoms  (post-exertional muscle weakness and neurological dysfunction), but a patient has  to experience at least eight symptoms to meet the diagnosis according to the  ME-ICC. Autonomic, sensory, and cognitive dysfunction, mandatory for the  diagnosis of ME, are not compulsory to meet the ME-ICC subcriteria for  'neurological impairments'. In conclusion, the diagnostic criteria for ME and of  the ME-ICC define two different patient groups. Thus, the definitions of ME and  ME-ICC are not interchangeable.