http://www.medscape.com/viewarticle/752984
"Our results support the possibility that genetically predisposed patients with Parkinson's disease may develop levodopa-induced vitamin B12 deficiency with subsequent neurotoxic methylmalonic acid accumulation," the authors report.

"In view of these data," the editorialists add, "we now need well-designed unselected population-based investigations and at best prospective epidemiologic studies, as well as experimental and clinical/electrophysiologic studies either demonstrating or refuting a direct causative link between levodopa exposure in idiopathic Parkinson's disease, neuropathy, and vitamin B12 deficiency or increased homocysteine and methylmalonic acid."

Meanwhile, what should be done for patients with Parkinson's disease?

The investigators call for clinical assessment of neuropathy in patients treated with levodopa on a long-term basis. They also recommend a classic workup including vitamin B12, homocysteine, methylmalonic acid levels in patients with confirmed neuropathy.

Finally, they suggest possible systematic B12 or folate supplementation.

Imad