Neuropathy in Parkinson disease: prevalence and determinants

Abstract

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.