Idebenone for Primary Progressive Multiple Sclerosis

Background: \- The Idebenone in Patients With Primary Progressive Multiple Sclerosis (IPPoMS) trial tested a new drug for multiple sclerosis. In the IPPoMS trial, participants took either idebenone or placebo. Researchers want to give idebenone to all participants for 1 year. It is still not certain whether idebenone can slow the progression of multiple sclerosis, but this study may help answer that question. Objectives: * To provide idebenone to all participants on the IPPoMS trial. * To collect data on the safety and effectiveness of idebenone for primary progressive multiple sclerosis. Eligibility: \- Individuals at least 18 years of age who have completed 3 years in the IPPoMS trial. Design: * The first study visit for this trial will happen on the same day as the last visit for the IPPoMS trial. * Participants will provide a blood samples and will have a lumbar puncture. They will also receive a new supply of idebenone to take three times a day with food. They will keep a diary to report on any side effects. * After this first treatment visit, participants will have two follow-up visits to the NIH 6 months apart. These visits may be scheduled over multiple days. Participants will provide blood and urine samples. They will also have imaging studies of the brain and spine. * Participants will have phone calls with the study researchers to provide updates on their condition and any side effects.