Dalfampridine After Optic Neuritis to Improve Visual Function in Multiple Sclerosis

Optic neuritis (ON) is the presenting feature of multiple sclerosis (MS) in 15% of cases, and occurs over the disease course in 50% of patients.1-3 Vision remains a major concern for MS patients, as visual dysfunction leads to lower quality of life.4-6 Despite the high prevalence of ON in MS, treatment and management options remain limited. Although intravenous glucocorticoids are employed to aid recovery of an acute episode of ON, no convincing evidence supports their efficacy in altering the degree of long-term recovery.7 Although some individuals with ON can have a dramatic recovery from blindness, ON often impairs visual function permanently. In the Optic Neuritis Treatment Trial, 63% reported that vision had not returned to normal after 6 months, and 20% had vision worse than 20/20 after 5 years of follow-up.8, 9 Visual impairment creates difficulties at home and work, leading to decreased independence and impaired mobility within the community. Visual dysfunction in combination with MS impairments within cerebellar and proprioceptive systems can be particularly disabling.

Optic neuritis classically impairs one's ability to read print or a computer screen, to drive in bright or low light, and to appreciate colors and contrasts. Unfortunately, when optic neuritis results in lasting impairment, there are no pharmacologic therapies to restore vision. Low vision specialists may provide magnifying glasses, brighter lights, and advice to optimize the position of objects at home and in the workplace. Better treatment options are needed to improve visual function.

Ampyra (dalfampridine) is a potassium-channel antagonist, with a mechanism-of-action to improve nerve conduction in demyelinated axons, resulting in an electrophysiologic and clinical benefit.10-22 Demyelinated axons within the anterior visual pathway would be a prime and ideal target to study the effects of Ampyra. In fact, Stefoski et al demonstrated visual function benefit in an open-label study of IV 4-aminopyridine in 12 subjects.21 The optic nerves are a well-defined white-matter tract, commonly affected in MS, and with clear clinical outcome measures. In addition, visual evoked potentials (VEPs) can be included within the study design as a secondary endpoint, to confirm improved nerve conduction. Because VEPs are such a precise, reliable, and accepted measure of demyelination, the anterior visual pathway is the ideal in vivo human system to study the electro-physiologic effects of a therapeutic such as Ampyra.

Hypothesis 1: Dalfampridine treatment will improve visual function, measured by the 5% ETDRS contrast sensitivity chart, in subjects with long-term visual impairment secondary to optic neuritis from MS.

Hypothesis 2: Dalfampridine treatment will reduce visual evoked potential P100 latency following remote optic neuritis.