Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a disease with unknown etiology, no validated specific and sensitive biomarker, and no standard approved effective treatment. ME/CFS has a profound impact on the quality of life of both patients and caregivers and entails high costs for society. The severity varies among patients who are able to participate to some extent in social life (mild), those who are mainly housebound (moderate) or bedridden (severe), and the very severely ill who are completely dependent on assistance for all daily living tasks, such as feeding or turning around in bed.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often starts in previously healthy individuals after an infection, the most common being infectious mononucleosis (EBV). It is more frequent in women and influenced by genetic predisposition. The main symptoms are postexertional malaise (PEM), fatigue, orthostatic intolerance, cognitive disturbances, sleep problems with inadequate restitution after rest, sensory hypersensitivity with pain, and symptoms related to autonomic and immune dysfunction. The prevalence is 0.1% to 0.8%, and ME/CFS must be distinguished from general fatigue, which is much more common in the population.