Updated November 30, 2014.
The main focus of research into autonomic dysfunction in Parkinson’s disease has focused on the heart and blood vessels via conditions such as orthostatic hypotension. However, autonomic disorders in Parkinson’s disease (PD) go beyond the heart and blood pressure.
Gastrointestinal Dysfunction
Gastroinstestinal complications of Parkinson’s have been recognized right from the very beginning. In the seminal 1817 paper written by James Parkinson, he described difficulty holding food in the mouth, insufficient saliva production, and constipation.
People with Parkinson’s disease may feel full too quickly, and even get nauseous after eating relatively little, as food does not move as quickly through the gastrointestinal system.
The gastrointestinal tract is encouraged by the parasympathetic part of the autonomic nervous system, which classically encourages us to “rest and digest.” Most of this stimulation comes from the dorsal motor nucleus of the vagus in the brainstem. This nucleus is one of the earliest places where Parkinson’s disease pathology can be detected after autopsy. Interestingly, alpha-synuclein (a protein commonly deposited in the brain in PD) can also be found within the nervous plexus of the stomach early in the disease course.
Symptoms do not seem to necessarily correlate with the amount of protein deposited, however—although constipation is a common early symptom, the colon is not as heavily impacted by protein deposits as the stomach. Medical management of constipation includes avoiding medications such as opiates which worsen constipation.
Increased fiber consumption is recommended (though this may worsen post-prandial hypotension).
Drooling is sometimes a distressing symptom in those with PD. Saliva production is not in fact increased—the problem is reduced swallowing, the mechanism of which is unclear. Treatments include local injections of botulinum toxin in to the parotid and submandibular glands, but may lead to worsened ability to swallow if the toxin diffuses to nearby muscles.
Swallowing problems occur in up to half of people with Parkinson’s disease. While the exact mechanisms are uncertain, the problem seems to relate to difficulty with the control even above the level of the brainstem nuclei. While there is no strong correlation with Parkinson's medication, some patients only note these troubles when “off” medication. Soft diets tend to help most forms of dysphagia.
Slow emptying of the stomach can contribute to feelings of abdominal distension and nausea. Small frequent meals can help. While drug like bethanechol can increase the contractions of the stomach, stomach contractions may not be well coordinated, and you may still have nausea and vomiting. Dopamine receptor blockers stimulate gastric motility, but that may worsen Parkinsonism. Domperidone is such a blocker that acts mainly outside of the brain-- however, it is not available in the United States.
Bladder Dysfunction
Urination is a surprisingly complex act. A survey suggested urinary abnormalities in about 95% of people with Parkinson’s disease. Detrusor hyperreflexia is the most common form, leading to urinary frequency, urgency, and urge incontinence, meaning a sudden irresistible need to urinate. Nocturnal frequency is common. Sleeping with the head of the bed elevated may help reduce nocturnal frequency in some patients. Anticholinergic mediations may also reduce detrursor contractions, but can worsen voiding problems and sometimes lead to urinary retension. They may also aggravate gastrointestinal problems and worsen cognition. As always, medications should be used with care.
Sexual Dysfunction
Sexual impairments are frequent in both men and women with PD. Up to 50% of men with PD have erectile dysfunction. Medications like sildenefil may be useful, but can worsen symptoms of orthostatic hypotension.
Sweating Disorders
Sweating is regulated by the sympathetic nervous system, though the effector neurotransmitter is acetylcholine instead of the noradrenergic transmitters used by the heart. Sweating in PD may be increased, decreased or normal. It is not known whether PD impacts the natural response to cold as well as heat.
As you see, there are several ways that Parkinson's disease can impact the autonomic nervous system, leading to a wide array of symptoms. No two people are likely to experience exactly the same problems, meaning that a tailored approach to treatment is required for each individual with Parkinson's disease and dysautonomia.
Source:
David S Goldstein Dysautonomia in Parkinson’s Disease Compr Physiol 4:805-826, 2014.
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