From what I have found I believe that Parkinson's Restless Leg Syndrome and Fibro may be related disorders.

Many of the same drugs work on all three disorders.
You get to many people that have two of these disorders. And some that get all three.

It looks like it depends on where in the nervous system that the damage is done which disorder you get If it is in the brain you get parkinson's. If in the brain stem or spinal cord you get fibro. And in the peripheral nervous system you get restless leg syndrome.

DOPAMINE seams to play a large role in all three disorders and dopamine is the main chemical that controls the levels of many of the other neuro chemicals.