“Could it not be a NMO, maybe I don’t even have MS,” the young patient asked me emphatically during the discussion about her medical history. I have been getting this question more often lately – and that is a sure sign that the existence of this disease has now reached patients.
The realization that the syndrome known as neuromyelitis optica (NMO, sometimes also referred to as Devic’s syndrome) is not a variant of multiple sclerosis, but a separate disease, has been known in the scientific world for over 10 years. In 2004, Vanda Lennon, a scientist at the prestigious Mayo Clinic, described an autoantibody as a serum marker that distinguishes NMO from MS.
Later, she was able to demonstrate that this antibody targets the water channel aquaporin-4. Since then, we have determined this so-called anti-aquaporin-4 antibody in cases that predominantly affect the spinal cord (myelitis) and the optic nerve (optic neuritis), in order to identify patients with neuromyelitis optica with its help. In the past few years, I had to ask intensively whether this laboratory value was determined, but now I am being confronted by patients with this question – that is, as I said, a good sign.
NMO is a rare inflammatory autoimmune disease of the central nervous system that almost exclusively affects the optic nerves and the spinal cord. NMO generally has a relapsing course with phases of longer stability between individual attacks, although the attacks can often be very severe. Inflammation of the optic nerve can lead to serious impairment up to blindness, the inflammation of the spinal cord is very extensive and covers three or more segments – we then also speak of a long-segment transverse myelitis (longitudinal extensive transverse myelitis, LETM). The response of an attack to high-dose cortisone is not always sufficient, sometimes only a blood wash leads to success.
Despite the similarity with the clinical symptoms of spinal MS, the two diseases can be distinguished by the detection of specific antibodies against aquaporin-4 – these antibodies are almost never present in MS. The distinction remains problematic in the one third of NMO cases that do not show these antibodies. Here, MRI can help, because typically NMO patients do not have classical MS lesions in the brain. Often the brain scans – despite severe clinical symptoms – are completely unremarkable. On the other hand, the typical long-segment lesions with clear swelling of the spinal cord can be found in the spinal cord. The cerebrospinal fluid can also help with the distinction – NMO patients usually have a more pronounced increase in cell count than MS patients and much less often show oligoclonal bands, which can be detected in about 90 – 95% of MS patients.
The diagnostic distinction between NMO and MS is of great importance, as the therapy for the two diseases also differs. For example, interferons can lead to a deterioration of NMO, and the administration of natalizumab (Tysabri® ) was rather less successful in NMO. Instead, B-cell depleting therapies have a good effect in NMO – currently rituximab appears to be one of the most effective means of treating NMO, even though it does not officially have approval for the treatment of NMO. However, there is consensus that this medication should be used consistently, especially when anti-aquaporin-4 antibodies are detected.
In conclusion, one should always think of NMO. Therefore, I advocate that the determination of the anti-aquaporin-4 antibodies should be included in the diagnostic clarification for MS initial diagnosis.
