Functional evaluation techniques in mitochondrial disorders.

Most of the mitochondrial disorders affect the brain and muscle metabolism with variable degrees of impairment. The diagnostic usefulness of the following physiological and imaging methods, which also offer functional information that can be used for follow-up, is critically assessed: lactate levels, exercise testing, phosphorus magnetic resonance spectroscopy (MRS), proton MRS, functional magnetic resonance imaging, positron emission tomography, optical tissue oximetry and single photon emission tomography. Knowledge of the advantages, shortcomings and results of each method in the evaluation of mitochondrial diseases is mandatory before they can be applied to other disorders with suspected oxidative impairment.