Parkinson’s disease (PD) is a progressive nervous system disorder known primarily for its effects on movement, such as tremor and rigidity. PD also produces a wide range of non-motor symptoms, many of which involve the digestive system. These gastrointestinal issues are extremely common and significantly impact the daily lives of people with PD. Addressing these non-motor symptoms is an important step in managing the overall disease experience.
Understanding Gastrointestinal Issues in Parkinson’s
Gastrointestinal (GI) symptoms affect a vast majority of PD patients, with estimates suggesting up to 80% experience digestive issues. While chronic constipation is the most frequently reported problem, diarrhea is also a recognized symptom. This irregularity is often categorized as dysmotility, which describes the irregular transit time of waste through the gut.
Diarrhea may occur as part of an alternating pattern of bowel habits, where constipation is followed by loose stools. It can also signal Small Intestinal Bacterial Overgrowth (SIBO), which affects a high percentage of PD patients. SIBO develops when slowed movement in the upper GI tract allows bacteria to flourish excessively, leading to symptoms like bloating, abdominal pain, and diarrhea.
Underlying Neurological and Medication-Related Causes
The neurological changes characteristic of PD are a direct cause of gut dysfunction, extending far beyond the brain. The accumulation of misfolded alpha-synuclein protein, the pathological hallmark of PD, occurs not only in the brain but also in the nerves of the gut wall, known as the enteric nervous system. This pathology disrupts the autonomic nervous system, which controls involuntary functions like the coordinated muscle contractions, or peristalsis, necessary for digestion. The resulting dysmotility slows the transit of waste, creating an environment ripe for digestive issues.
Overflow Diarrhea
A common cause of loose stools is a paradoxical reaction to severe constipation, known as overflow diarrhea. This occurs when a large, hardened mass of stool creates a blockage, and only liquid stool can leak around the impaction. Mistaking this for true diarrhea and attempting to stop it with anti-diarrheal agents can worsen the underlying impaction. A precise diagnosis is necessary before initiating any treatment.
Medication Side Effects
Medications used to manage PD motor symptoms are another frequent cause of diarrhea. Standard treatments containing Levodopa and Carbidopa can sometimes cause GI distress. COMT inhibitors, a class of drugs used to prolong the effect of Levodopa, are strongly associated with diarrhea, which can sometimes be severe and may appear months after starting the medication. Consulting a specialist to review the medication regimen is necessary when persistent diarrhea develops.
Management and Relief Strategies
Managing persistent diarrhea in PD requires an individualized approach that addresses the underlying cause. A medical professional, such as a neurologist or gastroenterologist, should first review all current medications to determine if a dose adjustment or change in drug class is warranted. Since overflow diarrhea is a possibility, it is advised not to use over-the-counter anti-diarrheal drugs without specific instruction, as they can exacerbate an impaction.
Dietary adjustments play a supportive role in regulating bowel movements. Maintaining adequate hydration is important to replace fluids lost during loose stools and prevent dehydration. Fiber intake should be managed carefully: soluble fiber helps absorb water and firm up stools, while excessive insoluble fiber might irritate the gut. Avoiding known GI irritants, such as excessive dairy if lactose intolerance is present, can also help minimize symptoms.
If SIBO is suspected, specific testing and targeted antibiotic treatment may be recommended to reduce the bacterial overgrowth. Incorporating moderate physical activity can stimulate gut motility and improve overall digestive health.