Comparison of plasma homocysteine levels and frequency of polyneuropathy in idiopathic Parkinsonian patients with healthy controls

Objectives: This study aims to compare the prevalence of polyneuropathy (PNP) in Parkinson’s disease (PD) and plasma homocysteine, vitamin B12, and folic acid levels with a healthy control group. Patients and Methods: Between January 2020 and June 2022, a total of 131 patients (67 males, 64 females; mean age: 62.3±12.7 years; range, 31 to 82 years) diagnosed with idiopathic PD and 83 (43 males, 40 females; mean age: 61.1±11.0 years; range, 34 to 78 years) age- and sex-matched healthy controls were included in the study. Demographic data, including PD duration, L-dopa (LD) dose and other medications, and Hoehn & Yahr (H&Y) stage were recorded for both patients and healthy controls. Sensory and motor nerve conduction studies, as well as plasma homocysteine, vitamin B12, and folic acid levels, were also measured in both groups. Results: The prevalence of PNP was 14.5% in the study group, while it was 4.8% in the control group. The prevalence of PNP increased, as the H&Y stage of PD increased in the study group. Plasma homocysteine and vitamin B12 levels were found to be significantly lower in the study group, compared to the control group. There was no significant difference between folic acid levels. When the patients with and without PNP was compared, plasma homocysteine, vitamin B12, and folic acid levels were found to be significantly lower. A significant association was found between the LD dose received by the patients and PNP, homocysteine, and vitamin B12 levels. Conclusion: Polyneuropathy is found to be associated with high homocysteine and low vitamin B12 and folic acid levels in PD patients. Polyneuropathy is common in LD-treated PD and is associated with high homocysteine and low vitamin B12 levels, likely reflecting an underlying impaired cellular methylation capacity. These findings should be confirmed in future large-scale prospective studies.