Neuropathy in Parkinson disease

Objective: To ascertain the prevalence and determinants of neuropathy in patients with Parkinson disease (PD), in particular, the roles of vitamin B₁₂ and levodopa exposure.

Methods: We performed a cross-sectional study of 37 patients with PD and 37 age- and gender-matched controls, using a sensitive and validated neuropathy scale. The prevalence of neuropathy was determined and compared between groups. We then ascertained the role of vitamin B₁₂ by a separate case-control analysis 1) comparing numbers of patients in whom the neuropathy was directly attributable to vitamin B₁₂ deficiency and 2) comparing serum vitamin B₁₂ levels in patients with PD with neuropathy with a second control group consisting of age- and gender-matched consecutive patients with neuropathy without PD. We also determined correlations between cumulative levodopa exposure, PD duration, neuropathy status and score, and vitamin B₁₂ status and levels in all patients with PD and, specifically, in those with neuropathy.

Results: Fourteen of 37 (37.8%) patients with PD and 3 of 37 (8.1%) control subjects had neuropathy (p = 0.005), corresponding to an odds ratio (95% confidence interval) for neuropathy, of 6.9 (1.78–26.73). Vitamin B₁₂ deficiency was a significantly more common cause of neuropathy (p = 0.024) and vitamin B₁₂ levels were significantly lower (p = 0.002) in patients with PD with neuropathy than in age- and gender-matched consecutive control subjects with neuropathy without PD. Cumulative levodopa exposure correlated with PD duration (p = 0.001) and vitamin B₁₂ levels (p = 0.044), in patients with PD with neuropathy.

Conclusions: Neuropathy is more prevalent in patients with PD than in control subjects. This may be predominantly due to vitamin B₁₂ deficiency, which could relate to cumulative levodopa exposure in susceptible individuals. Vitamin B₁₂ monitoring and supplementation, as well as serial clinical assessment for neuropathy, may be advisable in patients with PD.