Neuromyelitis optica – how is it different to multiple sclerosis?

If you have never heard of neuromyelitis optica (NMO), you’re not alone! NMO is a rare disease affecting the spinal cord and optic nerve. A disease is determined as rare when it affects less than 1 in 2000 people. NMO, Devic’s disease in layman’s term, is an autoimmune disease, which means the immune system fails and attacks healthy self-cells, and can be one-off or recurrent. When patients experience a NMO attack, symptoms like eye pain and weakness in limbs, caused by inflammation of the spinal cord (transverse myelitis) and optic nerve (optic myelitis), commonly occur. There is a much higher prevalence of females with NMO than males. The exact reasons are still being researched, but some suggest it could be due to hormonal, genetic, and epigenetic factors, including the gut microbiome. Currently, there is no cure to this sudden and perplexing disease, yet medication to suppress the immune system and reduce inflammation are prescribed to patients.

So the question arises – what causes NMO?

In short, we don’t know yet. However, we do understand that 90% of NMO cases are caused by NMO-specific antibodies against Aquaporin4 (AQP4), an intrinsic membranes protein highly concentrated in the spinal cord and the brain, specifically in astrocytes and ependymal cells lining in the ventricles. AQP4 are water-selective channels in many plasma membranes and are responsible for maintaining brain-water homeostasis. 

Did you know NMO is often mistaken as Multiple Sclerosis (MS)?

MS is also an autoimmune system and has similar symptoms as NMO, such as vision and mobility difficulties. However, there are important differences between the two. NMO specifically targets the optic nerves and spinal cord, leading to more severe attacks that can cause blindness and paralysis if not treated promptly. On the other hand, MS affects the brain and spinal cord more diffusely. Diagnosis and treatment for NMO and MS can be quite different, making it crucial to correctly distinguish between the two conditions. Advanced techniques like MRI scans, blood tests for specific antibodies (like AQP4-IgG for NMO), and careful clinical evaluation help doctors make the right diagnosis and provide appropriate treatment. Understanding these distinctions is vital for effective management and improving the quality of life for those affected by these diseases.

Written by Chloe Kam

REFERENCES

Hor, J.Y., Asgari, N., Nakashima, I., Broadley, S.A., Leite, M.I., Kissani, N., Jacob, A., Marignier, R., Weinshenker, B.G., Paul, F., Pittock, S.J., Palace, J., Wingerchuk, D.M., Behne, J.M., Yeaman, M.R. and Fujihara, K. (2020). Epidemiology of Neuromyelitis Optica Spectrum Disorder and Its Prevalence and Incidence Worldwide. Frontiers in Neurology, 11. doi:https://doi.org/10.3389/fneur.2020.00501.

Kim, S.-M., Kim, S.-J., Lee, H.J., Kuroda, H., Palace, J. and Fujihara, K. (2017). Differential diagnosis of neuromyelitis optica spectrum disorders. Therapeutic Advances in Neurological Disorders, 10(7), pp.265–289. doi:https://doi.org/10.1177/1756285617709723.

Mader, S. and Brimberg, L. (2019). Aquaporin-4 Water Channel in the Brain and Its Implication for Health and Disease. Cells, 8(2), p.90. doi:https://doi.org/10.3390/cells8020090.