Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 455

Gastrointestinal dysfunction represents a common manifestation of Parkinson’s disease⁶¹ and may both precede and predominate over the somatic motor symptoms.⁶² Involvement of the dorsal motor nucleus of the vagus may influence parasympathetic innervation, while abnormalities of the enteric nervous system (ENS) itself (such as Lewy bodies and loss of dopaminergic neurons) are also evident. Nevertheless, the pathophysiology of gastrointestinal complications of Parkinson’s disease has been insufficiently studied, and the relative contribution of loss of dopaminergic neurons in the ENS compared to defects of other aspects of neuronal function is unclear.

Dysphagia affects a majority of patients (50–90%), impairs quality of life, and tends to become more severe with the progression of the disease, although it does not always parallel the main neurological features.⁶³ Disturbance of the oropharyngeal phase of swallowing with impaired mechanosensitivity at the base of the tongue,⁶⁴ and impaired oesophageal transit associated with non‐peristaltic or tertiary pressure waves, are prominent. Heartburn is a common symptom and could be related to impaired acid clearance. The effects of L‐dopa and anticholinergic therapy on swallowing disorders are inconsistent; both drugs may be associated with either improvement or deterioration in dysphagia. Limited data indicate benefit from apomorphine, which is administered by subcutaneous infusion.

Gastric emptying is delayed in at least 70% of Parkinson’s patients attending neurological clinics, even in the absence of L‐dopa therapy, which is likely to slow gastric emptying further.⁶⁵ Delayed gastric emptying may contribute to the high prevalence of symptoms such as nausea and bloating and result in impaired nutrition and absorption of oral medications. In particular, L‐dopa may be metabolised to dopamine if retained in the stomach and unavailable for systemic absorption. In patients suffering from the ‘on‐off’ phenomenon of motor fluctuations, gastric emptying may normalise in the ‘on’ phase; conversely, variations in the rate of emptying may result in erratic L‐dopa absorption and thereby contribute to the on‐off phenomenon. Direct infusion of L‐dopa into the duodenum has been advocated as a solution to this problem, and it has also been suggested that the ratio of dopa decarboxylase inhibitor to L‐dopa be increased to improve the availability of dopamine peripherally as well as centrally.⁶² Metoclopramide is contraindicated in parkinsonian patients due to its effects on striatal dopamine receptors, but other prokinetic agents such as domperidone (which does not cross the blood‐brain barrier) can be used. Small‐intestinal, colonic, and anorectal dysmotility are also common in Parkinson’s disease and may be associated with bowel dilatation and constipation. Oro‐cecal transit time is prolonged compared with age‐matched controls.