Polyneuropathy while on duodenal levodopa infusion in Parkinson’s disease patients: we must be alert

Some reports have emerged describing the occurrence of Guillain-Barré syndrome and polyneuropathy related to vitamin B₁₂ deficiency in some patients with Parkinson’s disease (PD) treated with continuous duodenal levodopa infusion. We describe five PD patients who developed axonal polyneuropathy and vitamin B₁₂ deficiency while on treatment with duodenal levodopa infusion, review other cases reported in the literature, discuss potential etiologic factors, and suggest a possible algorithm for the management and prevention of this complication. One case of Guillain-Barré syndrome and at least 12 cases of polyneuropathy related to vitamin B₁₂ deficiency have been reported in PD patients treated with duodenal levodopa infusion. Levodopa gel infusion may induce a decrease in vitamin B₁₂ levels, leading to peripheral neuropathy. Additional pathogenetic mechanisms include alterations related to the metabolism of l-dopa, abnormal l-dopa absorption, and direct neurotoxicity of l-dopa at high doses. Vitamin B₁₂ supplementation may need to be considered in PD patients on duodenal levodopa infusion therapy. Vitamin B₁₂ deficiency in patients on duodenal levodopa infusion therapy may be more frequent than the published data suggest. We must be alert.