How Neurological Conditions Affect Bowel Function

The pathophysiology of Neurogenic Bowel Dysfunction (NBD) is much the same for spinal cord injuries, multiple sclerosis, and spina bifida, even though the nature of the damage differs.

Traumatic spinal cord injuries are usually well defined, whereas multiple sclerosis lesions may be found at multiple sites, and most patients with spina bifida have low spinal cord lesions, often at the conus medullaris or the cauda equina.

Spinal cord injury

Spinal cord lesions are classified as either located above the conus medullaris or located at the conus medullaris/cauda equina:

• A spinal cord lesion above the conus medullaris is an upper motor neuron lesion. It causes loss of voluntary control, maintains reflex activity in the anorectum, increased colonic transit time, and constipation. Anal tone is increased or maintained.
• A lesion at the level of the conus medullaris, the cauda equina, or the inferior splanchnic nerve is considered a lower motor neuron lesion. It causes loss of voluntary control, loss of reflex activity in the anorectum, prolonged transit time, constipation and rectal impaction, and reduced resting tone in the anal sphincter.
• Cauda Equina lesions result in parasympathetic denervation of the rectum and sigmoid colon and sphincters causing at atonic bowel, severe chronic constipation with overflow incontinence.

Spina bifida/myelomeningocele

The main problem is faecal soiling because of a lack of motor and sensory nerve input. This leads to problems with emptying the rectum because of pelvic floor weakness and descent preventing the stool from actually leaving the rectum.

The soiling is made worse by rapid and unopposed recto-anal inhibition and lack of sensation. If this is not treated effectively it can lead to a mega rectum.

As enemas flood back due to the inhibited anus a better treatment is surgery to enable washout via an ACE (antegrade continence enema). This allows fluids to be administered directly to the colon via an appendix stoma.

Multiple sclerosis (MS)

Constipation and faecal incontinence co-exist and are a source of considerable psycho-social disability.

Constipation is due to abnormalities of colonic activity and slow transit times (which makes the constipation worse).

Increasing dietary fibre can also make the constipation worse without sufficient fluids. Faecal incontinence can be due to:

• Impaired rectal sensation
• Difficulty switching on the mechanism for defaecation,
• Spasticity of the pelvic floor (digitalisation can assist evacuation)

Parkinson’s

Multifactorial causes (lack of exercise, chewing and swallowing problems) result in decreased bowel movements, frequency and defaecatory dysfunction, which can lead to incomplete evacuation.

Severe constipation which is often resistant to treatment may occur before first symptoms of Parkinson’s. Anti-Parkinson medication may slow transit time.

Colonic transit time is prolonged as a consequence of loss of dopamine within the CNS and the enteric nervous system. Increasing dopamine can help to treat the constipation.

Faecal incontinence may occur from disturbed anorectal reservoir or overflow secondary to constipation.

Stroke

Bowel dysfunction, constipation and faecal incontinence are common and distressing conditions after a stroke. Damage to the pontine-defaecatory centre can disrupt the sequencing of the sympathetic and parasympathetic nerves controlling defaecation causing incomplete bowel emptying. This results in impaired co-ordination of peristaltic waves and relaxation of the pelvic floor and external sphincter.

Other impairments which are common following a stroke may indirectly affect the bowel function:

• Mobility problems
• Communication problems (aphasia)
• Swallowing difficulties (dysphagia)
• Poor nutrition and insufficient diet due to chewing problems and dysphagia
• Dehydration and impaired thirst mechanisms
• Cognitive problems
• Mood changes
• Inability to self-toilet
• Inadequate force to defaecate (medications)

Cerebral Palsy

The name given to a group of lifelong conditions that affect movement and co-ordination caused by a problem with the brain that occurs before, during or soon after birth.

Cerebral Palsy is a neurodevelopmental disorder. Even though cerebral palsy affects muscle movement, it isn’t caused by problems in the muscles or nerves. It is caused by abnormalities in the cerebral cortex which controls muscle movements.

Constipation is the main bowel problem affecting individuals with cerebral palsy. Contributory factors relate to the cerebral palsy itself:

• Reduced fluids
• Diminished appetite and poor fibre intake
• Reduced mobility
• Impact of medications for seizures
• Weakness of muscles
• Difficulty co-ordinating defaecation
• Posture on the toilet

Treatment is to address the above factors. If the individual with cerebral palsy has normal cognitive function and is having difficulty with toilet training and has no physiological reason for having a problem, other factors should be considered.

The person with Cerebral Palsy may experience fear when using the toilet if they are insecure and are unsure of the toilet. Will they fall in? Might they fall off the toilet and hurt themselves? Cerebral Palsy, by itself, is very rarely the cause of a failure in toilet training or the ability to be continent.

Diabetes mellitus

Patients with diabetes may have faecal incontinence as a consequence of irreversible damage to the autonomic nervous system and impaired rectal sensation. Both motor and sensory dysfunction may occur.

The small intestine and diabetes

The enteric nerves supplying the small intestine may be affected leading to abnormal motility, secretion, or absorption. This leads to symptoms such as central abdominal pain, bloating, and diarrhoea.

Delayed emptying and stagnation of fluids in the small intestine may lead to bacterial overgrowth syndromes, resulting in diarrhoea and abdominal pain.

Enteric neuropathy may lead to a chronic abdominal pain syndrome similar to the pain of peripheral neuropathy in the feet.

People with diabetes have an increased risk of developing coeliac disease, which can lead to diarrhoea, weight loss and malabsorption, the coeliac disease responds well to a gluten-free diet but individuals may find adhering to both a diabetic and gluten-free diet difficult.

The large bowel and diabetes

Enteric neuropathy may affect the nerves innervating the colon, leading to a decrease in colon motility and constipation.

Diabetic diarrhoea is a syndrome of unexplained persistent diarrhoea in individuals with a longstanding history of diabetes. This may be due to autonomic neuropathy leading to abnormal motility and secretion of fluid in the colon.

There are also a multitude of intestinal problems that are not unique to people with diabetes but that can cause diarrhoea. The most common is the irritable bowel syndrome.

Individuals with diarrhoea often need to pass significant amounts of loose stool at night. The cause of diarrhoea is unclear. Neuropathy? Artifical sweeteners? Imbalance in enteric nervous system?