can you get them to do any nutrient testing? there are some nutrients in common between joint pain and ms.
i'd have a look at serum zinc, serum magnesium, and serum 25(OH)vitaminD3, if you can. they'll likely come back low normal.
if testing doesn't sound plausible, if you like you could send me a link to a specialty nutrition store accessible to you, and i'll see if I can pick some items for you to try out.
bahaha world without zinc https://www.youtube.com/watch?v=U1iCZpFMYd0