@anciendaze Do I remember correctly you looked for nervus vagus stimulation?
I have had an implant for years, but it was not for pain. It seems to have improved the balance between sympathetic/parasympathetic activity, which makes a difference in being able to sleep at night without drugs. (For some people that alone could be a life saver. None of us are much over 48 hours away from hallucinations and dangerous behavior caused by lack of sleep.) I'm convinced that most such studies are either dealing with the wrong patients, or are measuring the wrong things.
I take my own results as supporting a diagnosis of dysautonomia, which continues to affect me via orthostatic intolerance. (When well-regarded doctors still don't know what
Dr. Streeten did many years ago, and refuse to believe this, or to test for evidence, I don't have to look far for gaps in research protocols.) I don't think the implant is getting at the cause, but scarcely anyone seems to be doing much of anything that does affect possible causes.
The exceptions involve antivirals or rituximab. I believe most other therapies that show any effect are manipulating immune response, directly or indirectly, if they are not purely symptomatic. This is even true of some medications prescribed purely for symptomatic relief.
We still lack a mechanism for this pathology. Both classes of therapy I've mentioned are very general in their effects. Simply because a medication or therapy is done for particular indications is absolutely no evidence this is actually what it is treating. Example: Lithium salts used to treat AIDS-related dementia with mania didn't just calm patients,
they actually lowered viral titers.
Minocycline given for bacterial infections was also found to lower viral titers. In a rather different context, a substantial fraction of diabetics do not have low levels of insulin. I can recall when this was surprising news.
I remind people of the history of pyrotherapy for mental illness. The induced fever was a consequence of vigorous immune response to malaria, which happened to cross-react with
treponema pallidum, the cause of syphilis, a well-known cause of dementia, among many other problems. Medical professionals managed to misinterpret this in multiple ways.