Kidney disease, diarrhea, low sodium, pigmentation and epilepsy

Pls excuse my english, I'm european. Anyone with kidney disease whom also suffer from low sodium? I have this very rare condition in which my body will not contain sodium. If I add sodium orally I get severe stommach pain, need to have it intranevously. Also suffer with diarrhea when sodium is too low. I'm stuck in hospital and they can't give a diagnosis. I have epilepsy (since 5yrs) and are allready aware that Trileptal (and likes) can reduce sodium level. This is more complex than that. I have allways been low on sodium, even before epilepsy, but did'nt know until now. I think it was the other way around, that low sodium gave me epilepsy. But why do I have this sodium condition? I have pigmentation lines in handpalms and think it could be kidneys? Anyone?