Nerve Grafting for Parkinson's Disease or MSA

Inclusion Criteria: * Diagnosis of clinically established or clinically probable PD or MSA as defined by MDS criteria * Disease duration greater than 2 years * Age 40-75, inclusive * MDS-Unified Parkinson's Disease Rating Scale (UPDRS) Part III greater than or equal to 20 points but less than or equal to 35 points, off anti-parkinsonian medication for PD or MDS-Unified Multiple System Atrophy Rating Scale (UMSARS) less than or equal to 30 points off anti-parkinsonian medication * No MDS-UPDRS Part III score \>3 on items 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.14 while off medication * Able and willing to undergo ioflupane/SPECT * Able to tolerate the surgical procedure * Able to undergo all planned assessments * Available access to the sural nerve Exclusion Criteria: * Previous PD surgery or intracranial surgery * Ongoing major medical or psychiatric disorder incl. depression and psychosis * Other concomitant treatment with neuroleptics * Typical, nonparkinsonian syndrome ioflupane/SPECT signal * Unable to undergo an MRI * An obstructed trajectory path to the substantia nigra * Significant microvascular disease * Use of anticoagulants other than aspirin * Female who is pregnant, lactating, or of child-bearing potential unwilling to use an adequate birth control method during the period of the study * Consent capacity will be assessed and determined during and throughout a participant's neuropsychological exam. A participant who experiences a decline in consent capacity prior to surgery, will be removed from the study by the PI. A decline in consent capacity after surgery will not result in the removal of the participant in the study.