Motility Disorders of the Small Bowel

What is the small bowel?

To understand small-bowel motility disorders it is important to understand what the small intestine is and what it does.  The small bowel also known as the small intestine isn’t really “small” at all.  It is a long tubular structure that is 20-22 feet long. It is referred to as the small intestine because of the smaller caliber of the lumen (cross-sectional area) of the small intestine. It consists of 3 parts called the duodenum, jejunum, and ileum.  These are names that are given to parts of the small bowel so that we have ways of referring to the parts of the small intestine.  The duodenum is attached to the stomach, the jejunum is the part in the middle, and the ileum refers to about the last 3rd of the small intestine that eventually connects with the large intestine (colon).   The small bowel lies between the stomach and the large intestine or colon.  Slightly different functions occur within the different parts of the small intestine but the essential job of this part of the body is digesting and absorbing food as it passes through the bowel.

The small intestine consists of muscle cells and other cells that help absorb nutrients from food.  The small bowel depends on muscle movement otherwise known as “motility” to move the food through the gut.  The gut also has a sort of pacemaker within the wall called the migrating motor complex (MMC).  This migrating motor complex is responsible for strong repetitive contractions of the small bowel to move the food through the gut.  Intestinal muscle movement is also controlled by the enteric nervous system (ENS) and the autonomic nervous system (ANS).  The enteric nervous system consists of 2 series of circuits within the wall of the small intestine.  Once circuit lies underneath the lining of the part of the intestine that faces the food called the submucosa and the other circuit lies in the muscle layers of the small bowel.  Further adding to the complexity of intestinal motility and sensation is that the autonomic nervous system consists of the parasympathetic (controlled by the vagus nerve) and the sympathetic nervous system (controlled by the splanchnic nerves).  One way to imagine this is to think of the enteric nervous system as the electrical system that helps muscle movement and absorption of food through the small intestine and to think of the autonomic nervous system as all of the signals that are coming from the rest of the body so the small intestine knows how to work.  An important take-home point here is that both muscles and nerves control the movement of the small intestine.

What is a small-bowel motility disorder?

When a patient has a small bowel motility disorder, we mean there is a problem with the muscles or nerves that control movement in the small bowel.  The intestine behaves as if it is blocked but there no actual blockage. These kinds of disorders are very rare.  They can be divided into primary and secondary causes.  Primary types are genetic meaning they are there since birth and can be hereditary (passed down from mother to child). Sometimes people are just born with faulty nerve or muscle function from random gene defects (sporadic disorders).   Disorders that occur from damage to the nerves are called “neuropathies” and those that occur because of damage to the muscles are called “myopathies”.  These disorders are often referred to as chronic intestinal pseudo-obstruction (CIP).  Secondary causes are disorders that occur because of other diseases in the body like diabetes or Parkinson’s disease or connective tissue disorders like lupus or amyloidosis.  Sometimes disorders in muscle or nerve movement can happen of having a cancer. There are also infections that can cause damage to nerves.  And sometimes there are medications that cause a problem with nerve function.  Also damage to the muscles and nerves can occur because a patient is getting radiation to treat cancer.  About 40% of the cases of small bowel dysmotility are caused by genetic causes and the other 60% are secondary to other processes like infection, connective tissue disorders, cancers, drugs, and other diseases.  The table below summarize is the way of looking at these disorders.

Table 1 – Summary of Intestinal Motility Disorders and Causes

*Genetics can be – autosomal dominance, autosomal recessive, x-linked or sporadic.

What are symptoms of small bowel dysmotility?

Signs and symptoms may vary greatly from person to person and depend on the part of the GI tract that is most affected.  These disorders affect males and females in equal numbers.  The small bowel is the most affected area and patients can experience just chronic mild symptoms or there may more “acute attacks”.    The most common symptoms are nausea, vomiting, abdominal pain or cramping and bloating (abdominal distention) and constipation.  Abdominal pain can range from a dull aching to sharp stabbing pain.  Loss of appetite, getting full fast (early satiety) and weight loss are not uncommon.  A common complication is bacterial overgrowth in the small bowel (SIBO) which causes diarrhea. The small bowel doesn’t normally contain a lot of bacteria.   SIBO is covered else where in this education series.

Symptoms may be more minimal in childhood and progress over time to recurrent abdominal pain in adults, but the natural history of this disorder is still being worked out.  Other symptoms such as difficulty swallowing, heartburn, and chest pain as well as problems with the urinary bladder such as pain or difficulty with urination can occur as well. 

What tests are used to diagnose motility disorders?

There are a variety of tests that can be used to help figure out if there is a problem with motility and what is used depends very much on what we think the cause might be.  There are blood tests to detect infection or look for blood markers of auto-immune disorders like Systemic Lupus Erythematosus (SLE) or cancer related markers (Paraneoplastic antibody profile). 

There are different kind of x-rays that measure motility – nuclear transit studies and transit with markers that can be seen on plain x-rays.  Computerized tomography (CT scans) and magnetic resonance imaging (MRI) scans and plain x-rays can show changes of intestinal obstructions. X-rays with barium can also provide information on muscle movement

Flexible tubes that are inserted in the gastrointestinal (GI) tract to check muscle movement called manometers can evaluate the muscle movement in the esophagus or colon and even the small bowel (not used very often).  There is also a wireless motility capsule that measures transit through the entire GI tract.  Upper and lower endoscopies (EGD and colonoscopy) may also be used to take biopsies and rule out causes of blockage in the intestine.

Breath testing for bacterial overgrowth is commonly done to assess for bacterial overgrowth which is a complication of not having a lot of muscle movement in the small intestine.  This topic is covered elsewhere so it won’t be discussed in detail here.

On rare occasions full thickness small bowel biopsies are done

How are small bowel motility disorders treated?

Treatment of these disorders can be very complex and so only the broad concepts of care are covered in this section. The two biggest problems for patients with small bowel motility disorders are the lack of motility and a decreased ability to get the essentials nutrients that are needed from food.  Treatment may involve a combination of nutritional support and medications to help improve muscle or nerve function.  Nutritional support can range from specific diets that are low fiber and low fat, to feeding tubes into the stomach or small intestine to nutrition that is given into veins (total parenteral nutrition (TPN)).  Additionally, there are drugs that help promote muscle movement called prokinetics.  In cases of auto-immune diseases sometimes chemotherapy agents or medications that decrease inflammation are given (immune modulators).    Pain management may be necessary but opiate (narcotic medications) need to be avoided because they slow down the gut so neuromodulators that are used in disorders like irritable bowel syndrome may help.  Some complementary medications or techniques like safe herbal medications and visceral massage may be used.   One of the complications of lack of motility is that there is overgrowth of bacteria in the small bowel (SIBO – covered elsewhere) and antibiotics are used to treat that. In people with secondary CIP, treating the underlying disorder may help improve function.  For instance, if a patient has cancer treating the cancer may improve the problem with small bowel function. In some rare instances intestinal transplant may be possible.   Lastly investigational therapies like intestinal pacemakers are being evaluated.

It is always important to treat the whole patient so lifestyle habits like sleep and exercise and promoting good mental health are extremely important in these chronic disorders.  Much more information certainly needs to be discovered about these complex disorders and hopefully future research will open new diagnostic tests and treatments.