Imaging Systemic Dysfunction in Parkinson's Disease.

Parkinson's disease is now widely recognized to be a multisystem disorder affecting the brain and peripheral autonomic nerves. Extensive pathology is present in both the sympathetic and parasympathetic nervous system and the intrinsic gastrointestinal plexuses in patients. Autonomic pathology and symptoms such as constipation can predate the clinical diagnosis by years or decades. Imaging studies have contributed greatly to our understanding of Parkinson's disease but focused primarily on imaging cerebral pathology. However, given the importance of understanding the nature, chronology, and functional consequences of peripheral pathology, there has been renewed interest in imaging peripheral organs in Parkinson's disease. Suitable imaging tools can be divided into two types: radiotracer studies that directly estimate loss of sympathetic or parasympathetic nerve terminals, and imaging modalities to quantitate dysphagia, gastric emptying, esophageal and intestinal transit times, and anorectal dyssynergia. In this review, we summarize current knowledge about peripheral imaging in Parkinson's disease.