A 22 year-old female presents with onset of right eye vision loss 24 hours ago which has partially improved. She has experienced various widespread paresthesias, regional weakness and fatigue over the past six months. Episodes vary in location, severity and duration but invariably lead to recovery. Her exam is completely normal but MRI reveals numerous areas of periventricular gadolinium uptake. For this condition, what treatment has shown the greatest benefit with long term use?
A. Interferon beta 1a (Avonex)
B. Ethosuximide (Zarontin)
C. Methylprednisolone (Solumedrol)
D. Pyridostigmine (Mestinon)