Here I discuss why people with MS develop problems with their bowel function and I offer straightforward advice on how to manage constipation, diarrhoea and other MS-related bowel problems.

Key points

• Many people with MS experience a bowel disorder as a result of changes within the central nervous system that may affect the rectal and anal muscles.
• Agents that increase the muscular action of the bowel can help to treat constipation.
• Medications for some MS symptoms can increase constipation and may need to be reviewed.
• Faecal impaction associated with constipation is a serious problem that may need hospital treatment.
• Small intestinal bacterial overgrowth (SIBO) from faecal impaction may occur if the bacteria of the small intestine increase above normal values, producing harmful toxins.
• SIBO is associated with unpleasant symptoms including abdominal bloating, pain, anaemia, irritable bowel syndrome, constipation, diarrhoea and faecal impaction.
• Bowel hypomobility and any faecal impaction underlying SIBO need to be addressed, and antibiotics may be required to reduce the abnormal bacteria in the bowel. A gut health programme and dietary review are important for long-term management.
• Being incontinent of faeces in public is highly embarrassing and may lead to severe anxiety and social isolation.
• Faecal urgency or incontinence are best treated by developing a bowel routine and trying to evacuate your bowels in a controlled environment and at a regular time of day.
• Regular rectal or transanal irrigation can significantly improve the quality of life in such cases.
• MS should be treated early with effective DMTs, to avoid or delay damage to the neuronal pathways that control bowel function.

Many people with MS experience bowel disorders, including constipation, faecal hesitancy (difficult initiating a bowel action), incomplete emptying, faecal urgency, urgency incontinence, overflow diarrhoea, excessive bloating and excessive flatus. Understanding the causes of rectal and anal dysfunction in patients with MS can help us to select the most relevant therapies to target specific symptoms.

People with MS who experience constipation generally have a loss of sphincter tone (strength) at rest and during contraction compared with non-MS patients. In faecal incontinence, rectal sensitivity threshold is reduced, meaning that when faeces enter the rectum the threshold at which the defaecation reflex is triggered is lower than normal. There is also evidence that the coordination of the pelvic floor following contraction of the anal sphincter is abnormal in people MS. Pelvic floor exercises may help with this.

Management of constipation

Bowel dysfunction, particularly constipation, is common in MS. Constipation occurs because the MS bowel is sluggish due to reduced motility (i.e. the muscles or nerves do not work as they should). The management aim is usually to encourage regular bowel action, either daily or at least every two days.

Prokinetic agents that increase the muscular action of the bowel can help to treat constipation. The prokinetic agent I prescribe most often is senna. If this fails, other options include bisacodyl, co-danthrusate, sodium picosulfate or prucalopride; these agents work by stimulating the nervous system in the bowels. Prokinetic agents often need to be taken with bulking (fibre) and loosening (liquid) agents. Bulking agents include methylcellulose, psyllium or ispaghula husks, and sterculia granules. Loosening agents keep liquid in the bowel, causing water to be retained with the stool; examples include lactulose, polyethylene glycol (Movicol), magnesium hydroxide and magnesium sulphate (Epsom salts).

Cyclical use of laxatives can contribute to ongoing constipation: you use laxatives to treat your constipation, the laxatives cause diarrhoea, so you stop taking them. You then become constipated again, and the cycle repeats itself. 

If you experience bladder incontinence, dehydrating yourself to control your bladder problems can make constipation worse; you must drink adequate quantities of water throughout the day. Similarly, anticholinergic drugs used for treating urinary frequency and urgency and treatments for pain and spasticity may all make constipation worse. Therefore, if you are constipated your medications for other symptoms of MS need to be reviewed. 

Faecal impaction

Over time, the bowels may become impacted with faeces, and a hard, stony mass of compacted faeces forms (known as a faecolith). The gut bacteria may then overgrow and liquefy the stool above this impacted faecolith, bypass the impaction and cause diarrhoea. A typical history of faecal impaction includes periods of constipation punctuated by episodes of diarrhoea. If you suffer from chronic constipation and intermittent diarrhoea, you should contact your health team for help. Faecal impaction is a serious problem and often warrants treatment in hospital.

Below are some tips for managing MS-related constipation.

Small intestinal bacterial overgrowth (SIBO)

People with MS with bowel dysfunction may develop small intestinal bacterial overgrowth (SIBO), which is defined as an increase in the bacterial content of the small intestine above normal values. Some studies show that four in every 10 people with MS have SIBO; it is also detected in approximately one-third of patients with gastroenterological complaints who undergo a breath test. Proton pump inhibitors (omeprazole and related drugs) and smoking are risk factors for developing SIBO. The risk of SIBO increases with age and does not depend on gender or race.

SIBO is associated with dyspepsia, abdominal bloating, abdominal pain, anaemia, irritable bowel syndrome, functional constipation, diarrhoea and faecal impaction. A slowdown in your bowel transit time with SIBO decreases the normal clearance of bacteria from the small intestine. This slowdown is due to changes in the motility of the intestine, which is almost universal in people with MS.

Risks from SIBO

SIBO may damage the intestinal surface or mucosa of the bowel, because the bacteria can produce harmful toxins. This can result in leaky gut syndrome and acquired lactose intolerance. The leaky gut syndrome is controversial and associated with many symptoms that may overlap with MS-related symptoms. Leaky gut syndrome is not medically defined, and no specific tests or treatments are available. In comparison, acquired lactose intolerance occurs when someone loses the ability to digest lactose, the main sugar in milk, which causes them to develop diarrhoea, gas and bloating after eating or drinking dairy products. If you have lactose intolerance, you quickly learn to avoid lactose-containing products or use lactase preparations that help digest lactose. Please note that cheeses and yoghurt are generally tolerated because the bacteria used in the culturing process to produce these dairy products break down the lactose.

We know that many bacterial overgrowth products can impact human metabolism and behaviour. For example, people with liver dysfunction can’t metabolise these bacterial toxins and they develop hepatic encephalopathy. People with neurological disorders with reduced brain and cognitive reserve tend to be more susceptible to the effects of these bacterial metabolites, which are thought to upregulate innate immunity in the nervous system. This is why I try to stress to my patients that they should manage their constipation to prevent this from happening. Severe constipation and faecal impaction should be viewed as a chronic infection and managed and treated.

Diagnosis of SIBO

A breath test is most commonly used to diagnose SIBO. This noninvasive test measures the amount of hydrogen or methane you breathe out after drinking a mixture of glucose and water. A rapid rise in exhaled hydrogen or methane indicates bacterial overgrowth in the small intestine. Although widely available, breath testing is less specific than other tests for diagnosing bacterial overgrowth.

The gold standard for diagnosing SIBO is a small intestine aspirate and fluid culture. The fluid sample is obtained as part of a small bowel endoscopy. Other tests can include abdominal X-rays or CT scans. Faecal impaction resulting from constipation can also be diagnosed from spinal MRI scans of people with MS.

Management of SIBO

The initial way to treat bacterial overgrowth is to manage the underlying bowel hypomobility problem and clear any faecal impaction. In parallel, a course of antibiotics may be needed to reduce the number of abnormal bacteria in the bowel. However, unless you deal with the underlying problems, the bacteria will repopulate the bowel when the antibiotics are discontinued. This is why some people with SIBO may require long-term antibiotics. Switching between different antibiotics helps prevent bacterial antibiotic resistance from emerging. Please be aware that antibiotics wipe out most intestinal bacteria, both normal and abnormal; hence, they are not an ideal long-term solution to SIBO.

Starting a gut health programme is an essential part of treating SIBO. You will need a nutritional review, possibly with a dietitian, and you may need to change your diet to prevent constipation and/or faecal impaction. In some cases, you may require supplements. particularly if you are vegan.

Management of faecal incontinence

Being incontinent in public is one of the most embarrassing things that can happen to someone with MS, and it may result in social isolation to avoid experiencing the embarrassment again. Many patients with MS describe their experience of being incontinent of faeces and/or urine in public as the worst thing that has happened to them. It doesn’t have to happen; there are many ways to prevent it.

Faecal urgency needs attention (as does urgency incontinence – see section on bladder disorders). It is best treated by developing a bowel routine and trying to evacuate your bowels at a regular time of day, typically in the morning. This can be aided by using something to stimulate the bowels. I usually start by prescribing glycerine suppositories or mini-enemas. If the latter fails, I may elect to use transanal irrigation.

Transanal irrigation may sound drastic, but it often makes a massive difference to the quality of life in people with MS who need it and helps them to tackle a problem that can otherwise leave them stranded at home. I regularly refer patients for assessment to use the commercial rectal irrigation system, Peristeen, mainly because of the psychological benefits they derive from it.

The biggest problem with poor rectal compliance and faecal urgency is the odd occasion when you have diarrhoea due to gastroenteritis. With diarrhoea, whatever the cause, your rectum fills multiple times during the day and hence you are more likely to be incontinent. In this situation, you may need to use incontinence pads.

Faecal incontinence is not necessarily linked to disability. Why not? The reason is that a strategically placed MS lesion in the spinal cord can impact bowel function without causing other disabilities. I have patients who have had spinal cord relapses that leave them with faecal urgency and episodes of faecal incontinence, but very little other disability.

Case example

One patient of mine developed a severe anxiety disorder following an episode of faecal incontinence in public. She had intrusive thoughts and unpleasant flashbacks, reliving the episode repeatedly. After referral to a psychiatrist, she was diagnosed as having post-traumatic stress disorder. It took several years of counselling for her to overcome the social phobia associated with her anxiety and start going out again. She now ventures out only after having an enema to clear her lower colon and rectum; she never eats when she is out, so as not to stimulate the reflex urge to defaecate that follows eating. She wears pads and carries a change of clothing. Her faecal incontinence emergency pack contains wet wipes, clean underwear, spare continence pads and poo bags to dispose discreetly of any used items – the same items I packed when I went out with my daughters before they were potty trained.

The importance of managing bowel dysfunction

Bowel dysfunction is one of the hidden symptoms of MS. To assess whether or not you have a bowel problem, and its severity, you can complete the Wexner Incontinence Score. Over the lifetime of the disease, most people with MS develop bowel problems, so it is important to realise that much can be done to help you. Please discuss these symptoms with your neurologist or MS clinical nurse specialist. 

On the positive side, if MS is treated early and effectively before the neuronal pathways that control bowel function are damaged, these issues can usually be avoided or delayed. Preventing disability, such as bowel dysfunction, is better than treating it. This is another critical reason to manage your MS actively with DMTs.