Outcome Measures: Quantitative neuroimaging measures of central nervous system (CNS: i.e. brain and spinal cord) tissue destruction and clinical and functional (i.e. electrophysiological) measures of neurological disability will be collected every 6-12 months. Additionally, biomarkers focusing on analysis of reactive oxygen species (ROS) and oxidative stress will be collected every 12 months. The trial is currently powered using progression of brain atrophy as detected by SIENA methodology as the primary outcome measure. However, this may not be the most sensitive outcome available. In recognition of this, the trial has an adaptive design: i.e. it incorporates analysis of progression of CNS tissue destruction as measured by quantitative MRI markers and clinical/paraclinical markers defined as secondary outcome measures in the first 30 enrolled patients during the one year pre-treatment baseline, before randomization. All defined outcome measures collected in the first 30 enrolled patients will be transformed into z-scores and compared for the robustness of longitudinal change over the coefficient of variation. This will permit to select the most sensitive and most accurate outcome measure for detecting progression of CNS tissue damage. As a result, the primary outcome measure of this trial will be the comparison of individualized rates of brain atrophy progression between the idebenone and placebo groups after 2 years of treatment, unless the predetermined analysis of the pre-treatment baseline period in the first 30 enrolled subjects determines that one of the predefined secondary outcome measures has a higher z-score than brain atrophy measurement. In this case, the primary outcome would be the efficacy of idebenone versus placebo in inhibiting patient-specific slopes of functional or structural deterioration as measured by this more sensitive biomarker of CNS tissue destruction, yet to be defined by the analysis of the 1-year longitudinal data from pre-treatment baseline.