Transcutaneous Electrical Nerve Stimulation (TENS) for Lower Urinary Tract Disorders in Parkinson's Syndrome

The principal objective is to compare the efficacy of transcutaneous electrical nerve stimulation of the posterior tibial nerve with placebo stimulation, applied 20 minutes daily for 3 months, in Lower Urinary Tract Disorders (LUTD) in patients with Parkinson's disease or multisystem atrophy, evaluated using the PGI-I (Patient Global Impression of improvement) tool. The secondary objectives are to compare the efficacy of TENS with placebo stimulation on change before/after 3 months of treatment on: * the intensity of urinary symptoms, evaluated using the Patient Global Impression of Severity (PGI-S) scale * the number of voidings in 24 hours, number of episodes of urinary incontinence in 24 hours and maximum bladder capacity, evaluated by a voiding diary over 3 days * urinary symptoms, evaluated with the urinary symptom profile (USP) questionnaire * quality of life, assessed by the Qualiveen-SF® questionnaire * post-void residual volume measured by bladder ultrasound and effect on the development of infectious complications, by comparing the number of urinary infections over 3 months in each group. Lastly, the safety of TENS will be compared with that of placebo stimulation by the occurrence of adverse events during the 3 months of treatment.