A Study to Examine the Effect of Levodopa-Carbidopa Intestinal Gel (LCIG) Therapy Relative to That of Optimized Medical Treatment (OMT) on Non-motor Symptoms (NMS) Associated With Advanced Parkinson's Disease (PD)

1. Participant(s) must have a diagnosis of idiopathic Parkinson's disease according to the United Kingdom Parkinson's Disease Society (UKPDS) Brain Bank Criteria. 2. Participant(s) demonstrates persistent motor fluctuations in spite of individually optimized treatment. 3. The participant's Parkinson's disease is levodopa-responsive. 4. Participant(s) has had optimized treatment with available anti-PD medication and their motor symptoms are judged inadequately controlled on this optimized treatment. Optimized treatment is defined as the maximum therapeutic effect obtained with pharmacological antiparkinsonian therapies when no further improvement is expected regardless of any additional manipulations of levodopa and/or other antiparkinsonian medication. This will be based on the Investigator's clinical judgment. 5. Male or female participant(s) must be at least 30 years of age. 6. Minimum Parkinson's Disease Sleep Scale 2 (PDSS-2) total score of 18 at Baseline assessment.

1. Participant's PD diagnosis is unclear or there is a suspicion that the subject has a parkinsonian syndrome such as secondary parkinsonism (e.g. caused by drugs, toxins, infectious agents, vascular disease, trauma, brain neoplasm), parkinson-plus syndrome (e.g. Multiple System Atrophy, Progressive supranuclear Palsy, Diffuse Lewy Body disease) or other neurodegenerative disease that might mimic the symptoms of PD. 2. Participant(s) has undergone neurosurgery for the treatment of Parkinson's disease. 3. Known hypersensitivity to levodopa, carbidopa or radiopaque material. 4. Participant(s) has contraindications to levodopa (e.g. narrow angle glaucoma, malignant melanoma). 5. Participant(s) experiencing clinically significant sleep attacks or clinically significant impulsive behavior (e.g. pathological gambling, hypersexuality) at any point during the three months prior to the Screening evaluation as judged by the Principal Investigator.