NMO spectrum disorders: clinical or molecular classification?

The International Panel for NMO Diagnosis (IPND) released an updated set of guidelines for diagnosing Neuromyelitis Optica (NMO) and Neuromyelitis Optica spectrum disorders (NMOSD) in 2015.  We published a summary of the updated guidelines earlier on The TMA Blog. Diagnostic criteria for AQP4-IgG-positive NMOSD, NMOSD without AQP4-IgG or with unknown AQP4-IgG status were established, along with a set of core clinical characteristics to aid in diagnosing those with potential NMOSD. Anti-AQP4 antibodies affect the nervous system in a very specific way that is different from other auto-immune disorders to cause damage.

Another article by Uzawa et al. described the use of these guidelines in four NMOSD patients who were negative for AQP4-IgG. They found that the new criteria would be useful for more accurately diagnosing NMOSD earlier in patients. In this article, Dr. Pittock discussed Uzawa et al.’s findings and talked about the potential issues with diagnosing someone with NMOSD. He stated that what we call NMOSD might actually be several different diseases that we don’t understand enough about to identify them as different diseases. For example, the four NMOSD patients in Uzawa’s article though classified as NMOSD, had different symptoms, their MRIs looked different from each other, and their lab findings varied. Also, the way the immune systems of anti-AQP4 antibody positive individuals attacks itself is different from how the immune systems of people who are AQP4-negative attacks itself. By using symptoms and MRI findings to diagnose people with NMOSD, physicians might be clumping together people with different disorders that have different causes, prognosis, and different responses to treatment.

Pittock states that as more biomarkers are discovered, it might make more sense to name diseases based on the biomarker associated with them. Other autoimmune neurological diseases have done this when biomarkers have been found. He suggests using “autoimmune AQP4 channelopathy” instead of NMOSD. He also thinks that by classifying diseases in this way, it will be helpful as medications that target the specific immune process for each disease are developed.

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