Evaluating nerve disease in patients with Parkinson’s disease

This study investigated the causes of polyneuropathy (PN; damage of peripheral nerves that causes weakness and numbness) in patients with Parkinson’s disease. Researchers suggested that long-term levodopa treatment might be associated with PN in these patients.

Parkinson’s disease (PD) affects brain cells causing symptoms such as tremor and muscle rigidity. More recently, it has been shown that it also affects body nerves causing burning pain, numbness and weakness. The causes of PN are not fully understood.

However, recent studies suggested an association with the levels of homocysteine (HCT; a protein produced by the body) in the blood which is caused by long-term levodopa treatment. It is important to determine what causes PN in patients with PD.

This study included information about 125 patients with PD and 55 healthy similar individuals (control group). Of 125 patients, 28 were treated with levodopa for less than 2 years or not at all (group 1). 44 patients were treated with levodopa alone for 2 years or more (group 2). The remaining 53 patients were treated with both levodopa and entacapone for 2 years or more. PN and HCT levels were evaluated.

PN was more common in patients with PD than in the control group (18.4% vs. 7.27%). Group 1 of patients had similar rates of PN and levels of HCT compared to the control group. 29.55% of patients in group 2 and 15.09% of patients in group 3 had PN. Groups 2 and 3 had significantly higher HCT levels (20.14 µmol/L and 16.26 µmol/L) than group 1 (12.30 µmol/L) and the control group (11.81 µmol/L).

Patients who were treated at least one year with levodopa had a 52.6% higher risk of developing PN. Entacapone treatment at least 1 year lowered the risk of PN by 27%. An increase in HCT levels with 1 µmol/l increased the risk of developing PN by 36.4%.

This study showed that long-term levodopa treatment and increased HCT blood levels are risk factors for PN in patients with Parkinson’s disease. Entacapone treatment seems to protect patients from PN.

This study included a small number of patients. Larger studies are needed to confirm results.