Multiple sclerosis (MS) is a common disorder, characterized by inflammatory lesions of the CNS (brain and spinal cord), affecting approximately 0.15% of the population in the United States. The disease has a peak incidence in the second and third decades of life, typically presenting in this age group as relapsing–remitting disease (RRMS). Patients with RRMS present to the emergency department (ED) with acute exacerbations of their illness, as well as “pseudorelapses” relating to concomittent illness, often febrile. Good recovery from attacks is typically seen following the initial attacks. Attack frequency decreases with time, but many patients begin to accumulate permanent disability within the first decade after onset. In patients over 40 years of age, the disease presents commonly as a slow primary progressive illness (PPMS). Approximately 10–15% of patients have PPMS.