BACKGROUND: Chronic fatigue syndrome (CFS) or Myalgic Encephalomyelitis (ME) is characterized by neuro-psychiatric (e.g. depression, irritability, sleep disorders, autonomic symptoms and neurocognitive defects) and physio-somatic (fatigue, a flu-like malaise, hyperalgesia, irritable bowel, muscle pain and tension) symptoms. New ME/CFS case definitions based on consensus criteria among experts are largely inadequate, e.g. those of the US Institute of Medicine .
OBJECTIVES: The aim of the present study was to delineate a new case definition of ME/CFS based on pattern recognition methods and using neuro-immune, inflammatory, oxidative and nitrosative stress (neuro-IO&NS) biomarkers as external validating criteria.
METHODS: We measured the 12-item Fibromyalgia and Chronic Fatigue Syndrome Rating (FF) Scale in 196 subjects with CFS (CDC criteria) and 83 with chronic fatigue. The "Neuro-IO&NS" biomarkers were: IgM / IgA responses against LPS of gut commensal bacteria (leaky gut), IgM responses to O&NS modified neoepitopes, autoimmunity to serotonin, plasma interleukin-1 (IL-1) and serum neopterin.
RESULTS: Cluster analysis showed the presence of two well-separated clusters with highly significant differences in symptoms and biomarkers. The cluster with higher scores on all FF items was externally validated against all IO&NS biomarkers and therefore this diagnostic group was labeled "Neuro-IO&NS Fatigue" or "Neuro-Inflammatory and Oxidative Fatigue" (NIOF). An algorithm was constructed which defined NIOF as chronic fatigue and 4 or more of the following 6 symptoms: muscle tension, memory disturbances, sleep disorders, irritable bowel, headache or a flu-like malaise. There was a significant overlap between NIOF and CFS although NIOF criteria were much more restrictive. Factor analysis showed two factors, the first a fatigue-hyperalgesia (fibromyalgic complaints) and the second a fatigue-depression factor.