The purpose of this study is to determine if the drug eculizumab reduces the attack rate and improves outcome in patients with neuromyelitis optica.

It has been shown in some scientific studies that the the antibody marker specific for neuromyelitis optica (NMO), known as NMO-Immunoglobulin G (IgG), causes inflammation in brain tissues by activating a substance called complement. Complement can greatly increase the immune attack in the optic nerves (causing optic neuritis (ON)), spinal cords (causing transverse myelitis (TM)) and brains of patients with NMO. Eculizumab has already been shown to be effective in a rare blood disorder known as paroxysmal nocturnal hemoglobinuria (PNH). Attacks of PNH are also mediated through complement. Therefore, the investigators of this study are investigating whether by 'turning off' complement in NMO, further attacks of NMO can be prevented.

The primary (most important) objectives of this study are to determine:

Whether Eculizumab reduces relapse frequency in patients with relapsing NMO. The number of attacks during the one year treatment period will be compared to the number of attacks that occurred prior to initiation of eculizumab treatment. For patients with more than 2 year disease duration, the average number of attacks in the preceding 2 years will be calculated. For patients with less than 2 years disease duration the number of attacks in the preceding year will be used.

The safety profile of eculizumab in patients with NMO.

The secondary objectives are to determine:

Whether eculizumab maintains or improves walking, visual function and quality of life as measured by a variety of established disability scales. We will also assess the severity of an individual attack and the degree of recovery.

How the drug behaves in the patient's blood (called pharmacodynamics and pharmacokinetics).

Depending on our preliminary investigations we may evaluate patient cerebrospinal fluid in the laboratory to see how effective eculizumab is at getting into the cerebrospinal fluid from the blood stream, and to see if the drug reverses the biological effects of the NMO-IgG antibody.

Inclusion Criteria:

1. Diagnosis of NMO, as defined by 2006 criteria OR NMO seropositive spectrum disorder (Recurrent ON or longitudinally extensive transverse myelitis (LETM)). All patients must be NMO-IgG seropositive.
2. Clinical evidence of at least 2 relapses in last 6 months or 3 relapses in the last 12 months (with at least 1 relapse occurring in the preceding 6 months).
3. Age ≥18 years
4. Corrected visual acuity 20/100 or better in at least one eye. If fails item # 4 then entry allowed but only if last attack was myelitis and only attacks of myelitis are considered as outcome measurement.
5. Ambulatory (with or without walker). If fails item # 5 then entry allowed but only if last attack was ON and only attacks of ON are considered as outcome measurement.
6. Provision of written informed consent (see attached) to participate in the study.
7. N. meningitidis vaccination at least 14 days prior to receiving the first eculizumab infusion. If patient in midst of an acute relapse, then relapse will be treated with standard therapy and vaccination given only after a minimum of 4 weeks post attack onset.

Exclusion Criteria:

Candidates will be excluded from study entry if any of the following criteria are met at the time of randomization:

1. Progressive neurological deterioration unrelated to relapses of ON or myelitis.
2. Pregnant, breastfeeding, or intending to conceive during the course of the study
3. Patients will not participate in any other clinical therapeutic study or will not have participated in any other experimental treatment study within 30 days of screening
4. Patients with a history of splenectomy, because of a potential increased risk of developing meningococcal infection.