In answer to your first question as to how many have actually found a cause, I have.
The Neurologist that I went to was one sharp guy. He ran all the nerve test, etc. But then, he ran some blood test as well, and from the results, he recommended that I see a Hematologist that he knew. I agreed, and the Hematologist did some extensive, and I mean extensive, and expensive ($15,000) lab work. Results, with that and a bone marrow biopsy, he pinned down the culprit to a very rare, incurable cancer called Waldenstrom's Macrogloblunimia. Now, as soon as you get your tongue untied, I'll explain. WM is caused by an overpopulation of the white blood cell called IgM. Somehow, one of these suckers got screwed up upon being born, and came out with some wierd characteristics. Seems he can't die, like his brothers, and he acquired the ability to reproduce, and multiply. Normally, there are supposed to be around 350 of these guys in your bloodstream at any given time, all waiting to be called upon to fight off some intruder. At last test, I have some 7,100, and growing.

The first series of 4 infusions of a drug called Rituxan produced a drop in IgM level of about 800. That ain't gonna cut it. So the Dr. put me on a high dose of steroids for a month to lower my immune system, thereby giving the Rituxan a much better chance at doing a better job. From what I've learned on the internet, that is the recommended treatment regimen. That should drop the IgM by about a half, at least. I don't know where we will go after that. There's always chemo, plasmaphoresis, and a few other regimens that I have very little info on. Seems that most of the treatment for WM is gleaned from clinical trials, because that's all they have to go on. It isn't a disease that a lot is done for. Only about 3 people out of every 100,000 contract this disease.

So, to answer your first question, yes, in my case, a cause has been found, although I don't much like the diagnosis. Oh, by the way, for your information, the original problem that slowed up was, for me at least, peripheral neuropathy.
Initial symptoms, pain in my feet when I first put weight on them in the morning. That problem has progressed quite a bit. At this point, I have pain in both hands, as well as the feet, and a lot of muscle waste in one hand. Looks like the darn thing has been on a hell of a diet for the last year. Not a joking matter, I know, but better than wringing my hands, for sure. Typing this letter is one challenge, for sure. More correcting than typing. Last two fingers on right hand are beginning to curve more than stay straight. Keep hitting the wrong keys.

One thing that I have experienced that makes things better, and that's vitamins. I used to take vitamins religiously, but had gotten away from them for quite a while. As the PN got worse, I thought I'd better get back on them. I take Centrum, 1200 mg Fish Oil, Glucosamine Chondroitin, High potency B-Complex, as well as 1000 mcg of B12 daily. I find that when the PN gets bad, as it still does, it isn't AS bad as it used to be. And, the difference was almost instantly. As soon as I started back on the vitamins, the PN seemed more subdued, more masked. As if it was more in the background. Doesn't keep me from sleeping at night like it used to do. And, since the IgM level is still up in the clouds, that isn't what's making the difference.

Supposedly, when the WM gets in control, which the Hematologist tells me he'll make happen, the PN will go with it. And, with that, the various pains, and half a dozen bottles of expensive medicine. Now, that'll be the day. I have tried to "walk in your shoes", as they say, and consider what it would be like to have no cause to attack, to only look to pain management centers as your only recourse. With my limited "patience" I don't think I would survive for very long. I bow to your courage, and determination. I only hope you find the long sought answers, and that you are successful in treating the conditions.

Hope I've contributed something that will prove helpful. Take care.