Right you are Mariel; there is a prevalence of MS in the northern latitudes...however, it seems that some races, especially indigenous peoples in those areas, as well as in the far north are somehow immune to developing the disease.
That apparent racial distribution of immunity seems to indicate that there may be both a genetic factor (cause) linked to MS as well as an environmental one (condition).

Global Epidemiology and Prevalence of MS
http://library.med.utah.edu/kw/ms/epidemiology.html

With respect to detoxification and a possible familial genetic link, I think that you have hit at least one nail on the head. The Hutterites (German ancestors) as well as the Scandinavian Lapps also seem to be immune to MS and I do not believe that they are considered to be separate races from those of Caucasian European ancestry; the race which has the highest incidence of MS. Thus, along with racial prevalence, geographic distribution (and possible toxins in that area), there also seems to be a familial genetic link as well.

These are the sorts of things that I am finding difficult to ignore with respect to a "one cause-one cure hypothesis".
Even when we look at the Swank diet which has proven helpful for many, if we posit that such a diet is the only solution, then by default, it would suggest that those who consumed a diet that was at the opposite of the pendulum swing should or would have a higher risk of MS.
Yet, the numbers just don't agree with that potential theory.

For example, the modern Inuit and Native North Americans consume a diet that is high in saturated fat, high in processed carbohydrate and highly toxic due to the consumption of highly processed food and refined sugars; as most do not eat their native diets any more. Yet, these races have a very low incidence of MS, despite living in a highly prevalent area. But they might not have the seed of neuro0immune disease.

But similar to those races, the modern Lapp Scandinavian diet is very high in dairy, saturated animal fat, flour products and sugar; yet these people also seem to be immune to MS, again despite living among those who have one of the highest population distributions. Apparently they do carry the seed of neuro-immune disease, for they do develop it, just not as much as their bretheren in Scandinavia.

This sort of data is strongly suggestive of a genetic and familial link to prevalence as well as to immunity. At least so far, it does seem that MS and possibly other similar neuro-immune diseases arise due to possibly more than one cause (the neuro-immune disease seeds); such as genetics, gender & familial predisposition.
Further, it also seems that there may be a multitude of conditions including childhood vaccinations, virus exposure (especially in the pre-adult ages), toxicity and possibly a lack of enzymes that promote the 'sprouting and growth' of those neuro-immune disease seeds.

It is all such a head scratcher isn't it?

Please pass the enzymes, amino acids, vitamins, LDN, beta-interferons, steroids, antibiotics and what ever else might slow down the growth of the neuro-immune disease sprouts.
Lets bring them all out so we can all have a look at them...and maybe, just maybe, someone will finally figure out what will reliably work for whom and why.

With love, Erika