Why is NMO sometimes misdiagnosed as MS?

Question:
Why is NMO sometimes misdiagnosed as MS? How are the two so similar that a patient is originally diagnosed with MS, but years later, the diagnosis is changed to NMO Spectrum Disorder ?

Answer:
Neuromyelitis optica (NMO), also known as Devic's disease, is an autoimmune disorder in which immune system cells and antibodies mistakenly attack and destroy myelin cells in the optic nerves and the spinal cord. There are several reasons that patients with NMO are often misdiagnosed as Multiple Sclerosis:

1. Both MS and NMO are associated with acute optic nerve and spinal cord involvement. While there are differences, subtle and not so subtle, that can help differentiate the two conditions, there are many times when an initial or subsequent attack of NMO simply appears to be a severe MS relapse.

2. MRI scans of the brain can appear relatively normal in both NMO and early MS, although this is far less common an occurrence with a definite case of MS.

3. Spinal fluid oligoclonal bands may be absent early in the course of MS, and are usually absent in cases of NMO.

4. The antibody test we use to help diagnose NMO (anti-Aquaporin 4 Ig antibodies) is very specific but only has a sensitivity of 65 to 75 %. This means that more than 25 % of people with NMO with have negative results.

As you can see, most misdiagnoses occur early in the course of either condition. Therefore, the overriding reason for misdiagnosis is the urge to diagnosis MS too early (before it is possible) and failing to re-evaluate this diagnosis over time.  Generally, if an individual has a severe transverse myelopathy or optic neuropathy with incomplete recovery, especially in the setting of  longitudinally extensive white matter lesions in the spinal cord or optic nerve, neurologists should consider this a case of NMO until proven otherwise

Revere Kinkel MD
Director of the UCSD Multiple Sclerosis Program