Polyneuropathy in Levodopa-treated Parkinson's Patients

Recently published studies show that the prevalence of polyneuropathy (PNP) is higher in patients with Parkinson's disease (PD) than in age-matched controls. Its pathogenesis, however is a matter of controversy. The major hypothesis is the toxicity of high concentrations of homocysteine (Hcy) possibly related to levodopa (LD) therapy. The aim of the present study was to determine the prevalence of PNP, independent of other etiologies, and to determine the relationship to demographic and clinical factors in LD-treated Parkinson's patients. A total of 102 patients (51 patients with PD and 51 sex- and age-matched healthy controls) were enrolled in the study. The presence of any risk factors for PNP, ascertained from the history and laboratory tests, was an exclusion criterion. The Toronto Clinical Scoring System (TCSS) was used for clinical assessment of PNP. The objective assessment was based on electroneurography (ENG) studies in which motor nerves (peroneal and tibial nerves) as well as sensory nerves (sural and superficial peroneal nerves) were bilaterally examined. The severity of the disease was determined using the UPDRS scale (Unified Parkinson's Disease Rating Scale) and the Hoehn-Yahr (H-Y) scale. In the PD group, the clinical and neurophysiological indicators of PNP, manifested as a symmetrical and predominantly sensory axonal neuropathy, were more frequent then in the control group and observed in 43.1% vs. 13.7% and 15.7% vs. 2% of subjects respectively. The presence of PNP correlated with age and the severity of PD. Patients with PD and PNP had a higher level of Hcy as compared to PD patients without PNP, however the difference was not statistically significant. The frequency of PNP in PD patients is higher than in controls. The characteristics and discrepancy between the number of patients with clinical and ENG detected PNP may suggest the small fiber neuropathy (SFN) as the dominant form of neuropathy in PD patients.