I think the efficacy of coenzyme q10 for diagnosed PD is dependent upon the factors responsible for causing the disease or unmasking the disease. I know in my husband's case, the use of 1200 mgm/day of coenzyme Q10 resulted in incredible regression of symptoms--his masked facial expression abated, his shuffling walk was much less pronounced, the bradyknesia not as profound--the only thing it did not affect was the hand tremor. At this time, my husband was taking no anti PD meds. Just coQ10. If he misses a dose of coq10, he reports that he can feel the difference--his shuffle becomes worse, his posture becomes worse. etc. Placebo effect? I doubt it, since he does not deliberately miss the coQ10 dose--just gets busy or forgets it, and remembers when his symptoms increase.
The reason he originally took coq10 was due to the research we did on metabolic consequences of fat soluble lipitor---statins deplete coq10 levels as measured in plasma, platelets and muscle tissue. Perhaps the reason coq10 was so helpful for my husband was due to the fact that its depletion triggered the PD or exaccerbated the symptoms of PD.
Again, the problems with this study is that all PD patients are lumped together--difficult not to do when no true etiologic factors (except for genetic ones) are known. Patients like my husband may be the ones who truly benefit vs those whose PD is not linked to use of statins. He will continue taking it along with his now anti pd meds.