Large-Fiber Neuropathy in Parkinson's Disease: Clinical, Biological, and Electroneurographic Assessment of a Romanian Cohort.

(1) Background: Increased attention has lately been given to polyneuropathy in Parkinson's Disease (PD). Several papers postulated that large-fiber neuropathy (PNP) in PD is related to vitamin B12 deficiency and L-Dopa exposure. (2) Methods: Using a cross-sectional, observational study, we evaluated 73 PD patients without a previously known cause of PNP using clinical scores (UPDRS II and III and Toronto Clinical Scoring System), biological evaluation of vitamin B12 and folic acid, and nerve conduction studies to assess the prevalence and features of PNP. (3) Results: The prevalence of PNP was 49.3% in the study group. In the L-Dopa group, the frequency of PNP was 67.3% as compared to PNP in the non-L-Dopa group, where one subject had PNP (χ2 = 23.41, p < 0.01). PNP was predominantly sensory with mild to moderate axonal loss. Cyanocobalamin correlated with L-Dopa daily dose (r = -0.287, p < 0.05) and L-Dopa duration of administration (r = -0.316, p < 0.05). L-Dopa daily dose correlated with the amplitudes of sensory nerve action potentials of the superficial peroneal and radial nerves (r = -0.312, p < 0.05) (r = -0.336, p < 0.05), respectively. (4) Conclusions: PNP is more frequent in L-Dopa-treated patients than in L-Dopa-naïve patients. The results imply that longer exposure to high doses of L-Dopa may cause vitamin B12 and folate imbalance and PNP, secondarily.