Is Myalgic Encephalomyelitis (ME) an Neurological Disease?

First of all, let me say that Myalgic Encephalomyelitis (ME) is classified as a Neurological Disease (ICD 10 G93.3, or F286).

And I don't want to change that.

At least not now. Not until we know whether ME is one disease, or several distinct diseases, and until we know what the pathological processes at the root of ME are.

So regardless how ME is classified, what is the reality of ME? About that I want to speculate a bit.

Personally, I think it will turn out that the ME patient population, very much like CFS, will be composed of several diseases. Maybe there are, compared to CFS, less people who are (mis-)diagnosed with ME but have actually something else – but I doubt that ME is only one disease.

From the Norwegian Rituxan study by Fluge and Melle we know that a sizable portion of ME/CFS patients may have an autoimmune condition – which may or may not exclude neurologic problems to be the root cause. We can't tell from the Norwegian study one way or the other.

From the studies by Christopher Snell we know that VO2 max and exercise tolerance are reduced in a CFS patient population, which would point to cardiovascular causes, lung causes, or muscle-metabolic causes – a neurological root cause seems IMHO unlikely in the sub-group characterized by Dr. Snell, but still possible. The results from Dr. Snell are not particular specific and can be caused by different pathological processes, so there could be several diseases out there having the same VO2 max presentation (as seems already to be the case with other known non-CFS diseases).

From the studies by Kathleen and Alan Light we know that there are at least two sub-groups in the ME/CFS (and FM) patient population:

• People with a specific presentation of POTS like gene-expression
• People with a nonspecific presentation of fatigue and pain gene-expression

The specific POTS presentation may be indicative of a cardiovascular orgin, possibly with the involvement of endocrine system (beta-receptors seem to be implicated in a sub-group in the Lights studies). So the POTS sub-group IMHO may be one distinct disease, and I think it is unlikely to be several diseases.

The later sub-group (fatigue/pain) may IMHO most likely originate from metabolic problems in the muscle. It could be possibly caused by several pathways, which would possibly mean several distinct diseases.

These problems could in turn affect the brain in a negative way, showing up as neurological symptoms ("brain fatigue" or "brain fog", etc.)

So in conclusion, at the moment a sizable portion of patients seem to have a non-neurological root cause, especially hinted by the work of Kathleen and Alan Light.

Still, a minority of ME/CFS patients may be suffering from one (or more) – as of now – unknown and/or poorly understood neurological diseases – though it seems unlikely to me that a majority of ME/CFS patients have a neurological problem as root cause.

Of course, this does not preclude an neurological involvement in ME/CFS patients with non-neurological root causes.

This picture may change when more research brings us more data, until then we have to consider non-neurolgical etiologies for a majority of ME/CFS patients – I would not cling on to the neurological label forever.