Polyneuropathy in Parkinson’s disease and atypical Parkinsonian syndromes: clinical impact and risk factors

Polyneuropathy (PNP) is increasingly recognized as a comorbidity in Parkinson's disease (PD) but its prevalence, clinical features and impact in atypical Parkinsonian syndromes (APS) remain unclear. Understanding PNP in Parkinsonism is crucial for improving patients' mobility, slowing the disability progression and reducing disease burden. This study aims to characterize prevalence, etiology, and clinical relevance of PNP in PD and APS. Consecutive admissions of 104 PD, 52 progressive supranuclear palsy (PSP), and 27 multiple system atrophy (MSA) patients to the Department of Neurology at Hannover Medical School were analyzed. Assessments included Hoehn and Yahr stage, MDS-UPDRS III, electroneurography, PNP related conditions (e.g., diabetes mellitus, vitamin deficiencies), and PD drugs including levodopa equivalence dose (LED). PNP was highly prevalent across all three groups with a prevalence ranging from 37.0% and 47.1%. PD and PSP patients with PNP were older and predominantly male (p < 0.05). They also showed more advanced Hoehn and Yahr stages and higher MDS-UPDRS-III scores (p < 0.05). Sensorimotor axonal, length-dependent peripheral neuropathy was the most frequent presentation. We found no association between PNP and PD medications, and classic risk factors for PNP, such as diabetes mellitus, vitamin B12 deficiency, or chronic alcohol abuse, did not differ significantly between patients with and without PNP. Screening for PNP among patients with Parkinsonism, particularly among older males, is critical to optimize mobility. Further studies to identify the cause of the high prevalence of PNP among this population are needed.