In order to obtain comparative data for proper interpretation of the results in MS, two control cohorts one consisting of patients, the other of healthy volunteers will be studied. The patient control cohort will have three subcohorts: (1) patients with other disorders who are receiving DMT used in MS and are experiencing similar side effects (e.g. progressive multifocal encephalopathy (PML) in patients with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA)), (2) patients who are receiving DMT not used in MS but in whom MS-like illness is suspected (e.g. TNF-alpha inhibitors in patients with rheumatological diseases) and (3) patients with neurodegenerative diseases that may share pathophysiological processes with MS patients (e.g. oxidative stress in patients with Parkinson s disease or mitochondrial dysfunction in patients with mitochondrial diseases) and who do not qualify for the enrollment to the 09-N-0032 protocol. Enrollment of patients with different diseases who are experiencing identical side effects on DMTs as those studied in MS cohort will help to answer the question of whether the identified mechanism of action of the side effect is MS specific or generalizable. The other neurological disease cohort will provide data to assess the specificity of the MRI findings in the MS cohort.