Ampyra for Optic Neuritis 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.

Hypothesis 3: Dalfampridine treatment will result in an improvement in secondary endpoints, including visual fields, high contrast visual acuity, color vision, and quality of life.

The study will be conducted at the Department of Neurology and Neurosurgery, Washington University School of Medicine, St. Louis, the institution at which Dr. Naismith is based. The MS patients will come from the 1800 active MS patients in our clinic and the 3500 in the St. Louis area.

Fifty subjects will be enrolled in this Phase II, investigator-initiated, randomized and blinded cross-over trial of dalfampridine of 8 weeks duration (Table 1). The study will test the hypothesis that dalfampridine, when administered to subjects with incomplete visual recovery after optic neuritis from MS, will result in symptomatic improvement in visual function. The study will consist of one screening/baseline visit, one visit during treatment with active drug, and one visit on placebo. After the baseline visit, subjects will be randomly assigned to receive study medication or placebo for the first three weeks, followed by a two week wash-out, and then treatment reallocation for the latter three weeks.

Inclusion criteria

are:

• At least one previous clinical episode of optic neuritis,
• the last episode of ON must have occurred at least 12 months prior to study entry,
• clinically definite MS, defined by the revised McDonald criteria, 23
• ages 18-70,
• visual acuity greater than or equal to 20/30
• must be able to read at least 2 of the 5 letters on the top line of the 5% ETDRS chart (logMAR 0.96) at 3 meters, 2 meters or 1 meter, and
• must have sufficient cognitive function to understand the consent process and to reliably perform all clinical assessments

Exclusion criteria

are:

• Any ophthalmologic condition, other than ON, which can affect vision, including nystagmus in primary position of gaze,
• history of seizures or spells with altered level of consciousness,
• pregnancy or breast feeding,
• an MS exacerbation or use of glucocorticoids within 3 months of entry,
• a history of moderate to severe renal insufficiency,
• previous use of 4-aminopyridine, in any formulation, in the prior 4 weeks.