Polyneuropathy in Parkinson's Disease is Highly Prevalent and Not Related to Treatment

An increased prevalence of peripheral polyneuropathy (PN) in Parkinson's disease (PD) associated with greater functional impairment has previously been reported. A possible cause has been suggested as levodopa therapy. The aim of this real-world study was to assess the prevalence and the characteristics of PN in PD and to investigate the putative association between PN and oral levodopa.

A cohort of 692 consecutive patients with idiopathic PD had routine clinical, laboratory, and lower limb clinical neurophysiology assessment when attending the certified tertiary Parkinson center, Schön Klinik Neustadt, Neustadt in Holstein, Germany, between 2016 and 2019. Patients were sent by general neurologists for the medication adjustment, physiotherapy, ergotherapy, and logopaedic treatment. A retrospective cross-sectional review of the data was performed.

The mean age of the cohort was 72.6 (8.44) years (range, 44-90 years) and 60% were male. The age of the first PD manifestation was 65.22 (10.09) years (range, 31-88 years). Of 692 patients with PD, 507 (73.27%) had clinical signs of neuropathy and PN was first diagnosed 6.3 (5.7) years after the PD onset. Of these 507 patients, 446 (87.96%) underwent the electrophysiological investigations with PN confirmed in 396 patients (88.79% out of 446 electrophysiologically investigated patients with PD). Peripheral polyneuropathy was ruled out in 50 patients (11.21% of 446 electrophysiologically investigated patients with PD). The half of patients had moderate and severe sensory axonal PN (201 patients or 53.03% of all 396 with confirmed PN). The mean motor examination part of the Movement Disorders Society's Unified PD Rating Scale score in patients with PN was significantly higher (off, 30.48 [11.60] points; on, 19.92 [10.27] points), than in patients without PN (off, 27.17 [14.57] points; on, 17.14 [11.98] points), with P < 0.01 in the both off and on states. The mean levodopa daily dosage was similar in patients with PN and without PN (565 mg vs 556 mg, P = nonsignificant). No difference between other dopaminergic medication in PN and non-PN group was found.

PN is highly prevalent in patients with PD. There was no association between oral levodopa or other dopaminergic medication and PN. More awareness of PN in PD clinics and further understanding of the pathophysiology, which leads to the development of an axonal polyneuropathy in PD, are required.