Neuromodulation For Constipation
Cats and humans share a common problem: constipation.
Cats and humans share a common problem: constipation. Sedentary lifestyles, suboptimal fluid and fiber intake, and uncontrollable stress all contribute to digestive difficulties. Neither drugs nor surgery alleviate the ailment entirely. Each poses risks of future morbidity and continued distress of one sort or another.1,2 Even something as seemingly harmless as an herbal enema can deliver damaging consequences. A recently published case report recounts how a “natural” enema nearly killed a patient by causing massive rectal hemorrhage.3
At least humans can usually control the cleanliness and quality of the bathrooms they seek, the food they eat and the water they drink. Cats cannot. No one enjoys a dirty, smelly latrine; similarly, cats dial down their interest in eliminating when faced with a putrid litter box already overflowing with feces. Cats have specific preferences for low, sometimes clear glass bowls without the odor or taste of other cats’ mouths in the water or on the sides of the container. Add in the worry of being watched or ambushed while defecating, pain in the pelvis or spine,4 and the cacophony of household noise and agitation,5 and one may be well on the way to producing a chronically constipated cat.6
Narcotics such as tramadol and diuretics only contribute to the problem.7 A popular motility modifier, cisapride,8 is at times becoming difficult to procure. Longstanding constipation may lead to megacolon and long-term debility.9 While most cases of megacolon fall into the “idiopathic” category, the real culprit may be a disturbance within the enteric nervous system (the intrinsic nerve network within the intestines) or a disruption in the capacity of the various central and autonomic nervous system regulatory centers to restore gut homeostasis and healthful motility.
The Defecation Reflex
Successful elimination requires an intact defecation reflex. Neurons governing this distal digestive impulse originate in the brain and spinal cord, coalescing in the distal colon, rectum, and anus. Under normal circumstances, this region responds to the presence of feces by issuing visceral afferent input to sacral spinal cord segments. The cord then sends efferent signals to the intestines, impelling the large bowel to evacuate its contents by means of highly synchronized contractions in the smooth muscle of the colon and rectum. At this point, the internal anal sphincter and caudal paraspinal muscles should relax through involuntary means. In preparation for defecation, the individual then consciously relaxes the external anal sphincter and increases intra-abdominal pressure. This is known as the Valsalva maneuver. Defecation ensues, unless...
Pain can interrupt this tightly regulated sequence at any point. Memory of past pain while defecating can cause a cat to retain feces to avoid hurting by voluntarily contracting the external anal sphincter.10 Feces return to the colorectal region and wait for the next defecation reflex. Over time, rectal capacity and compliance increase, possibly producing megarectum or a perineal hernia, further complicating an already frustrating disorder.
Any number of issues can upset the sympathetic and parasympathetic balance needed for normal motility. Certainly, a diagnostic workup and appropriate environmental and husbandry changes should be instituted for the constipated cat. If these fail, however, drugs and surgery are not the only options, and veterinarians should consider neuromodulating these cats. Neuromodulation influences spinal processing of pelvic afferent signals. It modifies cerebral activation and modulates output from brain centers that govern anorectal function.11,12
Early attempts at neuromodulation left some constipated patients dead. Lumbar sympathectomies from the 1940s had a 2.5 percent mortality rate.13 Today, methods have become much kinder, gentler and less invasive. They include electrical nerve stimulation,14 acupuncture,15 massage, laser therapy and even microbes.
Microbes as Motility Modifiers
Microbes? Indeed! Gut bacteria shape the neuronal data that intestinal nerves send to the brain.16 These “voices from within” give the vagus nerve blow-by-blow accounts of the status of the digestive environment. This information has the capacity to modify brain activity, mood and behavior. It would be hard for the brain to ignore their collective input, as the human gut, for example, houses 1-2 kg of microbiota, equating to 100 trillion bacteria, 1800 genera, and up to 40, 000 species. Our nervous system “listens to our gut” with the assistance of 500 million neurons. “Good guy” bacteria, i.e., probiotics, soothe our psyche with analgesic input by altering the intensity of contractions and the excitability of extrinsic spinal primary afferent terminals that supply the gut mucosa.17 Microbes may make us feel anxious or depressed, giving new meaning to “gut feeling” and “gut reaction.”18
Other forms of neuromodulation include sacral nerve stimulation (SNS). One can influence pelvic reflexes through acupuncture, or other percutaneous, transforaminal methods that activate the nerves implicated in intestinal slowdown.19 A number of studies have reported on the effectiveness of SNS for motility disorders in constipated humans.20 SNS improves appropriate sensation from the pelvic floor and viscera, anal sphincter function and colonic motility. Acupuncture or nerve stimulation at other sites influences brainstem-based vagal parasympathetic pathways that regulate gastrointestinal motility and coordinate reflexes.21 Cats who become reluctant to defecate due to pain from disk disease in the lumbosacral region22 or elsewhere may find that acupuncture and related techniques reduce this pain and help restore normal elimination patterns.
Massage for a Happy Belly
Swedish massage for constipation has enjoyed wide popularity across the U.S. and Europe from the 19th century onward. Recently research emphasizes its value and explores its mechanisms of action. Like acupuncture, massage yields changes in enteric and central nervous system activity.
Abdominal massage encourages peristalsis, decreases colonic transit time, increases the frequency of bowel movements in constipated patients, and reduces the discomfort and pain of chronic constipation.23-25 The mechanism of moderate pressure massage involves dermal and/or subdermal pressure receptors supplied by vagal nerve afferents. These fibers project to the nucleus tractus solitarius in the brainstem, a somatoautonomic convergence center that regulates vagal nerve output.26 Abdominal massage may stimulate gut mechanoreceptors directly and aid in initiating motor action. Motivated and educated clients can learn simple, easy-to-teach abdominal massage techniques that strengthen their emotional ties and effectively improve elimination habits when studied in humans.27,28
Neuromodulation First, Surgery Last
Considering the range of nonsurgical options for constipation, a variety of options should be tried early on and well before submitting a cat to surgery. But first, make sure the cat has everything else she needs to develop and maintain health bowel habits, especially a clean the litter box and privacy. After all, no one likes an audience in the bathroom or a dirty toilet.
1. Kenefick NJ. Sacral nerve neuromodulation for the treatment of lower bowel motility disorders. Ann R Coll Surg Engl. 2006;88(7):617-623.
2. Bosshard W, Dreher R, Schnegg J-F, et al. The treatment of chronic constipation in elderly people – an update. Drugs Aging. 2004;21(14):911-930.
5. Tache Y, Martinez V, Million M, et al. Stress and the gastrointestinal tract III. Stress-related alterations of gut motor function: role of brain corticotropin-releasing factor receptors. Am J Physiol Gastrointest Liver Physiol. 2001;280:G173-G177.
6. Houston DM. New medical and nutritional approaches for managing feline constipation, obstipation, and megacolon in cats. Small Animal and Exotics Proceedings. Book One: Alternative medicine - Ophthalmology. North American Veterinary Conference, Orlando, Florida, USA, 14-18 January 2012. Volume 26; Gainesville: The North American Veterinary Conference, 2012.
11. Iwa M, Nakade Y, Pappas TN, et al. Electroacupuncture elicits dual effects: stimulation of delayed gastric emptying and inhibition of accelerated colonic transit induced by restraint stress in rats. Dig Dis Sci. 2006;51:1493-1500.
15. Iwa M, Matsushima M, Nakade Y, et al. Electroacupuncture at ST-36 accelerates colonic motility and transit in freely moving conscious rats. Am J Physiol Gastrointest Liver Physiol. 2006;290:G285-G292.
21. Chen J, Song G-Q, Yin, J, et al. Electroacupuncture improves impaired gastric motility and slow waves induced by rectal distention in dogs. Am J Physiol Gastrointest Liver Physiol. 2008;295:G614-G620.