Levodopa-Induced Neuropathy: A Systematic Review

Background: Background Clinical, neurophysiological, and pathological evidence suggest an association between Parkinson’s disease (PD) and peripheral neuropathy (PNP), with a possible causative role of levodopa metabolic products, such as homocysteine and methylmalonic acid. Methods: Methods We conducted a systematic review of studies reporting cases of PNP in L-dopa-treated PD patients indexed in PubMed between January 1990 and March 2018. Results: Results We identified 38 articles reporting cases of PNP in PD patients treated with oral L-dopa or with L-dopa/ carbidopa intestinal gel infusion (LCIG). Prevalence of PNP was 30.2% in the former group and 42.1% in the latter. Oral L-dopa was mostly associated with slowly progressive PNP, whereas LCIG showed an acute or subacute onset in 35.7% of cases. In both groups, there was an association between PNP and higher L-dopa doses, as well as with the following biochemical alterations: increased homocysteine; reduced vitamin B12; increased methylmalonic acid; and reduced vitamin B6. A skin biopsy was performed in 181 patients, showing signs of small fibers neuropathy in 169 (93.4%). Positive, yet preliminary, results were observed in patients receiving periodic vitamin supplementation. Conclusions: Conclusions Over one third of PD patients in treatment with L-dopa may develop PNP, with a significantly higher prevalence of acute and subacute forms in those receiving LCIG. Pathogenic mechanisms remain unclear, but possibly related to a complex interplay between peripheral neurodegenerative processes and L-dopa neurotoxic metabolites. Prospective, randomized, clinical trials are required to identify factors associated with the onset and progression of PD-associated PNP and clarify the protective role of B-group vitamin supplementation.