Gastrointestinal System in Myotonic Dystrophy

Print this page

Symptoms

Gastrointestinal (GI) symptoms are common, disabling and potentially serious features of myotonic dystrophy (DM) that result from dysfunction of alimentary tract skeletal or smooth muscles:

  • chewing and swallowing difficulties due to mouth, tongue or throat weakness or myotonia
  • gastroesophageal reflux (heartburn) caused by esophageal sphincter laxity
  • abdominal or chest pain (dyspepsia), nausea, vomiting, bloating or bowel pseudo-obstruction due to ineffective peristalsis
  • cholestasis (gall stones) due to ineffective gall bladder or bile duct musculature
  • constipation, diarrhea or malabsorption caused by bowel dysmotility (with secondary bacterial overgrowth), potentially causing fecal impaction, megacolon, bowel perforation and sepsis
  • impaired or painful bowel movements (dyschezia)
  • fecal incontinence due to anal sphincter and pelvic floor muscle weakness
Form     
Sign and Symptoms

Congenital DM1

Prenatal:

  • Polyhydramnios - accumulation of amniotic fluid in the mother caused by reduced ingestion of amniotic fluid by the fetus

Newborn:

  • Ineffective nursing and failure to thrive, due to weak suck and ineffective swallow caused by craniofacial skeletal abnormalities and weakness of face, tongue, and jaw muscles

  • Aspiration – inhalation of ingested liquid or secretions due to pharyngeal weakness and in coordination, potentially causing aspiration pneumonia.

Childhood/Teen Years and Adulthood:

  • Ineffective swallow (dysphagia) caused by craniofacial skeletal anomalies, or weakness, incoordination and myotonia of face, tongue, jaw, esophagus, and throat muscles

  • Aspiration due to pharyngeal weakness, potentially causing pneumonia

  • Recurrent post-prandial abdominal pain and bloating due to ineffective peristalsis or bowel pseudo-obstruction

  • Constipation, diarrhea, irritable bowel syndrome, caused by ineffective peristalsis or secondary intestinal bacterial overgrowth

  • Gall stones, due to abnormal gall bladder, bile duct, or sphincter musculature

  • Dilated colon, potentially leading to stool impaction, bowel perforation or megacolon

Childhood Onset DM1 and Adult Onset DM1

  • Difficulty swallowing (dysphagia) caused by weakness or myotonia of the face, tongue, jaw, esophagus, and throat muscles.

  • Aspiration due to pharyngeal weakness potentially causing pneumonia.

  • Recurrent abdominal pain and bloating, especially post-prandially

    Constipation, diarrhea and irritable bowel symptoms

    Gall stones due to abnormal muscle function of the gall bladder, bile duct and sphincter

  • Dilated colon, which can result in fecal impaction, possibly associated with megacolon or bowel perforation and sepsis

DM2

  • DM2 patients commonly have gastrointestinal symptoms, including constipation, diarrhea, irritable bowel complaints, post-prandial bloating and abdominal pain, or gastroesophageal reflux, but additional investigations are required to determine whether these features, and their molecular and cellular causes are similar

 

 Diagnosis

Careful assessment of the digestive tract is essential to relieve symptoms and to avoid secondary effects and complications. Gastrointestinal symptoms often develop gradually so that patients adopt compensatory mechanisms and consequently avoid necessary examinations. Patients and physicians can thus be unaware of gastrointestinal dysfunction until it comes to clinical attention due to acute exacerbation. For example, mild bowel dysmotility can be overlooked until a patient presents with symptoms of advanced pseudo-obstruction, at which time misdiagnosis of the severe abdominal pain and bloating as a complete mechanical bowel obstruction can lead to the potentially disastrous consequences of inappropriate abdominal surgery. This situation can be avoided only by conscientious and detailed inquiry about gastrointestinal problems at the time of routine clinical care, investigating, treating and educating patients at an early stage rather than when symptoms climax in an acute abdomen.


Routine gastrointestinal assessment should include:

  • History and review of symptoms, specifically detailing difficulty with chewing (myotonia or fatigue), swallowing (dysphagia for solids; aspiration of liquids, or frequent dry cough suggesting aspiration of secretions), gastroesophageal reflux, frequency of meals, post-prandial symptoms of bloating or pain, characteristics of any abdominal pain, frequency and character of bowel movements, occurrence of fecal or urinary incontinence.
  • Routine physical examination, specifically noting evidence of involuntary weight loss, dysphonia indicative of pharyngeal weakness, frequent cough indicative of aspiration, abdominal pain on palpation either generally or at gallbladder, abdominal bloating.


In symptomatic individuals additional evaluation should include, as appropriate:

  • Abdominal X-ray to evaluate abnormal bowel gas or stool, or free abdominal air
  • A swallow study can characterize dysynergic movements, pharyngeal weakness, pharyngeal or esophageal constriction, or aspiration
  • Abdominal ultrasound, or if necessary MRI scans, can detail stomach, small bowel, large bowel or gall bladder anatomy.
  • Barium upper GI radiographic evaluation can assess lower esophageal function and reflux, gastric emptying, and small bowel anatomy and function. If acute bowel obstruction is considered, a barium radiographic investigation with small-bowel follow-through distinguish pseudo-obstruction from the surgical emergency of true bowel obstruction.
  • Manometry can demonstrate weakness or disordered contraction of esophagus, gastroesophageal sphincter, stomach, small bowel, rectum and anal sphincter.
  • Endoscopy can define abnormal structure or function of pharynx, esophagus, stomach, small intestine or large intestines.
  • Blood tests done to investigate cholestasis or hepatic involvement need to be interpreted cautiously - transaminases (AST and ALT) cannot be considered “liver function tests” in part because they are released by either damaged muscle or liver, and thus are commonly elevated in myotonic dystrophy due to the muscle disease. Similarly, gamma-glutamyltransferase (GGT) blood level does not correlate with liver damage in myotonic dystrophy because it too is often elevated in all DM1 and DM2 subjects. Alternatively, serum alkaline phosphatase and bilirubin elevation do correlate with cholestasis in myotonic dystrophy.

Treatment

A primary therapeutic tenet, to do no harm, is critically important in treating GI symptoms of myotonic dystrophy patients. Painful bowel dilitation caused by myotonic dystrophy pseudo-obstruction, but mistakenly diagnosed as an acute bowel obstruction, can lead to needless abdominal surgery that not only exposes patients to the risks of anesthesia and surgery (potentially lethal in myotonic dystrophy patients with cardiac and ventilatory dysfunction), but also can cause post-operative strictures that greatly complicate management of intestinal dysmotility in myotonic dystrophy patients. Alternatively, clinical or radiographic verification of pseudo-obstruction can prevent surgery and lead to appropriate conservative management with pro-kinetic peristaltic agents, decompression, hydration, and avoidance of narcotics, which exacerbate hypomotility.

Chronic symptomatic treatment can reduce GI symptoms in myotonic dystrophy:

  • Mexilitene can reduce myotonia in muscles of mastication that interfere with chewing, or in pharyngeal and proximal esophageal muscles responsible for dysphagia.
  • Prokinetic drugs (such as metoclopramide, and erythromycin), can intermittently reduce symptoms of bowel hypomotility (bloating, abdominal pain, constipation), though tachyphyllaxis prevent their chronic utility
  • Cholestyramine can treat diarrhea, incontinence, and pain; interestingly, prokinetic agents can sometimes help control diarrhea that results from the bacterial overgrowth that is caused by hypomotility and malabsorption


In addition to pharmacologic approaches such as mexilitene, treatment of dysphagia can include:

  • dietary modification (mechanically soft foods are easiest to swallow)
  • involvement of a speech therapist to teach behavioral and postural modification (e.g., neck flexed when swallowing, reduction of mouthful volume, alternation of solids and liquids, use of a particular implement, such as a cup, straw or spoon that improves swallowing)
  • gastrostomy feeding to maintain nutrition and protect the airway (nasogastric tubes are typically contraindicated in myotonic dystrophy patients because they increase risk of aspiration).

View a list of references for this page.