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A recent overview of neurocognitive research  into ME/CFS found that attention span, memory and reaction time were impaired, a finding that is consistent with the memory and concentration problems that patients themselves complain about. Given that some neuropsychiatric disorders also show similar cognitive symptoms, there is a need to identify specific biomarkers to differentiate ME/CFS as a distinct biomedical disease.

Magnetic resonance spectroscopic imaging is a relatively new technique that gives information about metabolic changes in the central nervous system. The patient is placed inside a powerful magnet which magnetises atoms in the body, causing them to line up. A short radio frequency pulse alters this arrangement, and as the atoms spring back into alignment, a magnetic resonance signal is produced. This signal is analysed to determine the concentrations of various chemicals in the body tissue, and the information across a region can be collected together to form a two-dimensional image.

Researchers in New York have used this method to measure levels of a metabolite called lactate in the cerebrospinal fluid (the liquid that surrounds the brain and spinal cord) in 19 ME/CFS patients, 31 people with major depressive disorder (who can have impaired concentration, sleep and appetite) and 23 healthy control subjects. Significantly, they found that mean lactate levels were higher in the ME/CFS group (0.92 units) than in the healthy volunteers (0.04), while the depressive disorder group had an intermediate level (0.40). Moreover, the researchers found a significant correlation between lactate and mental fatigue in ME/CFS patients, but not in depressed patients or healthy controls.

The scientists point out that high brain lactate levels are consistent with reports of areas of low blood flow to the brain in ME/CFS patients, and also with reports of increased oxidative stress in ME/ CFS leading to mitochondrial dysfunction, anaerobic glycolysis and lactate production.

Reference: Increased ventricular lactate in chronic fatigue syndrome measured by 1H MRS imaging at 3.0 T. II: comparison with major depressive disorder. Murrough JW, et al. NMR Biomed 2010 Jul; 23(6): 643-50.