Peripheral neuropathy in idiopathic Parkinson's disease: A systematic review.

Background: Parkinson's disease (PD) has been associated with peripheral neuropathy (PN). PN has been demonstrated in some rare genetic forms of PD (e.g. PARK2 mutations) but has also been linked to levodopa exposure.

Objective: The aim of this systematic review is to clarify any evidence of peripheral nervous system involvement in idiopathic PD.

Methods: A systematic computer-based literature search was conducted on PubMed database.

Findings: The pooled estimate of the prevalence of large fiber PN in PD was 16.3% (based on 1376 patients). The pooled estimate of the prevalence of biopsy-proven small fiber neuropathy was 56.9% (based on 72 patients). Large fiber PN in PD is in the majority of cases distal, symmetrical, axonal and predominantly sensory. There are, however, few reports of chronic idiopathic demyelinating polyneuropathy and very occasional cases of acute neuropathies. Although nerve conduction studies have been performed in the majority of the studies, they included only a limited number of nerves, mainly in the lower limbs. There is little evidence to support a direct link between levodopa treatment and the development of PN in idiopathic PD. In the majority of the cases PN has been linked to abnormalities in vitamin B12, methylmalonic acid or fasting homocysteine levels. Additional aetiological risk factors for PN may be responsible for any apparent link between PD and PN.

Conclusions: Large-scale prospective studies with long-term follow-up with detailed baseline assessments are needed in order to understand the natural history of PN in PD, both on clinical and neurophysiological parameters.