Peripheral neuropathy (PN) has been reported in idiopathic and hereditary forms 
of parkinsonism, but the pathogenic mechanisms are unclear and likely 
heterogeneous. Levodopa-induced vitamin B12 deficiency has been discussed as a 
causal factor of PN in idiopathic Parkinson's disease, but peripheral nervous 
system involvement might also be a consequence of the underlying 
neurodegenerative process. Occurrence of PN with parkinsonism has been 
associated with a panel of mitochondrial cytopathies, more frequently related to 
a nuclear gene defect and mainly polymerase gamma (POLG1) gene. Parkin (PARK2) 
gene mutations are responsible for juvenile parkinsonism, and possible 
peripheral nervous system involvement has been reported. Rarely, an association 
of parkinsonism with PN may be encountered in other neurodegenerative diseases 
such as fragile X-associated tremor and ataxia syndrome related to premutation 
CGG repeat expansion in the fragile X mental retardation (FMR1) gene, 
Machado-Joseph disease related to an abnormal CAG repeat expansion in ataxin-3 
(ATXN3) gene, Kufor-Rakeb syndrome caused by mutations in ATP13A2 gene, or in 
hereditary systemic disorders such as Gaucher disease due to mutations in the 
β-glucocerebrosidase (GBA) gene and Chediak-Higashi syndrome due to LYST gene 
mutations. This article reviews conditions in which PN may coexist with 
parkinsonism.