Gastrointestinal dysfunction in Parkinson's disease.
Gastrointestinal dysfunction is common and clinically important in patients with PD. Evidence continues to accumulate to indicate that these symptoms reflect, for the most part, the direct involvement of the gastrointestinal tract by the PD process. Gastrointestinal symptomatology may arise not only as a consequence of the effects of PD on skeletal muscles in the oropharynx, anorectum, and pelvic floor but also through the direct involvement of the autonomic and enteric nervous systems in the PD process. While many aspects of gastrointestinal dysfunction in PD continue to be delineated, therapeutic approaches to gut symptoms in this common disorder remain in their infancy. Gut involvement in PD can be seen to serve as a paradigm for gut-CNS interactions. The recent demonstration of neuropathologic abnormalities in the enteric nervous system analogous to those regarded as pathognomonic of the parkinsonian process in the CNS suggests that the enteric and central nervous systems may demonstrate parallel pathologic changes in a number of disease processes previously regarded as confined to the central and somatic nervous systems. In this way, the enteric nervous system may well serve as a more accessible "window" to a variety of degenerative neurologic disorders. With respect to PD itself, we can begin to relate both the neurologic and gastrointestinal manifestations of this disorder to defects at a number of levels (Table 1).