Fulminant multiple sclerosis (MS) is the most malignant form of MS which usually leads to death in few weeks. Although it can be accompanied by optic neuritis (ON), but long interval between ON and the grave onset has not been reported. Fulminant MS usually occurs as the first onset and previous ON is not common. We report a rare case of 30-year-old woman with a history of ON 1 year ago. The rapid deterioration to vegetative state followed by a seizure and previous ON differentiated this case from previous reported cases. The differential diagnosis of a rapidly progressive leucoencephalopathy in this patient includes inflammatory, vascular, infectious and toxic disorders. Regarding the previous history of optic neuritis with positive brain MRI (multiple T2 hyperintense lesions in white matter) in our patient, multiple sclerosis is the most probable diagnosis. More effective treatments, such as plasmapheresis and cyclophosphamide, that influenced on the prognosis of some previous patients could be useful, but should be performed before progressive brain atrophy emerges.