Overview

Myotonic dystrophy is a disease that results in musculoskeletal weakness. It usually presents itself in adulthood and is a progressive multisystem genetic disorder. Based on the clinical presentation, it can be subdivided into two groups– Myotonic dystrophy type I (DM1), known as Steinert disease, and myotonic dystrophy type II (DM2), or proximal myotonic myopathy. In the European population, myotonic dystrophy is the most common type of muscular dystrophy. DM1 is more common than DM2.  Globally, muscular dystrophy has an incidence of 1 per 3000 individuals.¹

Dysphagia is the difficulty in eating, drinking, and swallowing food and it may affect 1 in 17 people in their lifetime.² Dysphagia is one of the most difficult symptoms associated with muscular dystrophy (typically DM1). It causes weight loss, increased tiredness,  weakness of the muscles, aspiration pneumonia, or even sudden death.³ Hence managing dysphagia in people with myotonic dystrophy is critical.

Understanding Myotonic dystrophy

Myotonic dystrophy is an autosomal dominant genetic disorder which usually begins at adulthood. It is usually inherited from one of the parents. Very few cases occur without family history.  A gene mutation (change) within the  DMPK gene causes DM1, whereas mutation in another gene called CNBP causes DM2.⁴

Myotonic dystrophy results in generalised weakness of the skeletal muscles. DM1 (Steinert disease) is the most common type seen in adults, whereas DM2 (proximal myotonic myopathy) is rarer and the symptoms occur later in life. The symptoms of DM2 are also found to be milder than DM1. 

Based on the clinical signs and symptoms, patients with myotonic dystrophy type1 (DM1) can be divided into three subtypes.

• Congenital DM1

Usually presents before birth as increased levels of amniotic fluid in the womb (polyhydramnios) and reduced foetal movement. After birth there will be generalised weakness, respiratory compromise, reduced movements, characteristic fish shaped upper lip, feeding difficulties, club feet, delay in achievement of milestones, cardiac problems etc.

• Childhood onset DM1

Characterised by facial weakness, difficulty in speech, hand muscle myotonia, low intelligence, and psychological problems. They often go undiagnosed in early childhood due to the lack of neurological problems and negative family history.

• Classical adult onset DM1

This is the most common subtype and is associated with distal muscle weakness, especially in the hand and foot muscles, as well as ankle and facial muscle weakness, difficulty in opening eyes, weakness of neck muscles etc. Muscle weakness progresses slowly in such cases.⁵

Myotonic dystrophy type 2 (DM2) is an autosomal dominant disorder characterised by myotonia (90%) and muscle weakness (82%). It usually begins in the third decade of life and is associated with muscle pain, stiffness, tiredness and muscle weakness especially on the neck, hip and elbow.⁵

Symptoms and diagnosis

The characteristic feature of myotonic dystrophy is myotonia, the delayed relaxation of the muscles. This results in generalised weakness of the muscles, fatigue, and excessive drowsiness. Other symptoms include arrhythmia, cardiomyopathy, sleep apnoea, hypopnoea, cataract, drooping or falling of upper eyelid, dermatitis, delayed gastric emptying, constipation, and diarrhoea due to bacterial overgrowth.⁶ It is also associated with endocrine disturbances such as  primary testicular failure, diabetes, insulin resistance, dysregulated calcium metabolism, and thyroid problems.⁷ One of the most problematic symptoms associated with DM1 is dysphagia, which is the difficulty in swallowing food, and may lead to several complications. 

The diagnosis of myotonic dystrophy is through a thorough medical and family history, physical examination, genetic testing, serum creatinine kinase, hepatobiliary function testing, muscle biopsies, and electrocardiographic findings for cardiomyopathy.¹

What is dysphagia?

Swallowing is the process of entry of food from the oral cavity into the stomach. It is divided into two phases. The first phase is the preparation of food into a bolus in the mouth, while the second phase is pushing the bolus by the tongue towards the oesophagus. This phase is very rapid and the upper esophageal, pharynx, and the suprahyoid muscles must act synchronously for swallowing to be effective. In myotonic dystrophy, there is often weakness of these muscles, as well as  the tongue muscles. Furthermore,there is also weakness of the muscles involved  in chewing,  all of which results in the lack of coordinated activity resulting in dysphagia. 

The link between Myotonic dystrophy and dysphagia

Swallowing is a complex procedure that involves the muscles of tongue, mouth, pharynx, larynx, and oesophagus. The different stages of swallowing include oral, pharyngeal, and esophageal stages, according to the location of the food bolus. The oral stage is subdivided into oral preparatory and oral propulsive stages. 

The anticipatory stage is the stage before the food is taken into mouth. In the preparatory stage, the food is prepared into a food bolus by tongue, teeth and soft palate. At the end of the oral stage the food bolus is transported into the pharynx, from the mouth. In the pharyngeal stage, the food bolus is transported through the pharynx and into the oesophagus by an involuntary movement called peristalsis. In the esophageal phase, the food is transported by the peristaltic movement of the muscles into the stomach.⁸

In Myotonic dystrophy, all of the stages of swallowing are affected. Some patients show poor awareness of dysphagia in the anticipatory stage. In the preparatory phase, the forces of the chewing muscles and the strength of the lip and cheek muscles are reduced, leading to the swallowing of food without adequate chewing. In the pharyngeal phase, the peristaltic movement  and the ability of the epiglottis to close the windpipe reduces. Often, the cough reflex threshold becomes high, leading to silent aspiration of food. In the esophageal phase, the peristaltic movement of muscles is reduced. Combined,this leads to difficulty in swallowing  food and can result in regurgitation of food.⁹

Different studies have reported a 25% to 80% prevalence of dysphagia in myotonic dystrophy patients.¹⁰ 

Symptoms and signs specific to Myotonic dystrophy-related dysphagia

Symptoms may appear either in the early stages or in the later progressive phase. It includes:

• Difficulty initiating swallowing
• Slow eating–seen in early phase
• Difficulty in pushing food by the tongue in the mouth
• Difficulty in chewing food
• Drooling of saliva
• Oronasal regurgitation
• Coughing and choking during eating
• Nasal regurgitation
• Recurrent aspirations
• Aspiration pneumonia
• Malnutrition and dehydration

Diagnosis and evaluation

Medical history and physical examination

The problems associated with gastrointestinal tract may sometimes be so gradual that the patient might be adapted to it without awareness. A thorough medical history is often required to elicit the recall of symptoms. Physical and neurological examinations will also be done.

Diagnostic tests

The diagnostic tests include swallowing assessment such as videofluoroscopic swallow study (VFS), an X-Ray made after drinking a contrast material called barium, endoscopy, Fiberoptic Endoscopic Evaluation of Swallowing (FEES), or Manometry.

A VFS uses X-Ray to visualise the mouth, pharynx and oesophagus. FEES uses a camera at the end of a flexible tube passed through the nostrils to get an image of the pharynx and oesophagus. A manometry is an esophageal muscle test in which a small tube connected to a pressure recorder is used to measure the muscle contraction while swallowing.¹⁰

Role of Specialists

Speech and language pathologists can help in the assessment and management of swallowing difficulties. They assess the medical history, face, mouth and throat muscles, and make observations while the patient is eating and drinking. They then decide whether an instrumental assessment like videofluoroscopy or  FEES is required. If required, they may refer the patient to a neurologist, gastroenterologist, or a psychologist.

Treatment and management

Dietary modifications

• Try to avoid the food that you may find difficult to chew and swallow.
• Adapt and make texture modifications to the difficult food like cut crusts off bread, dunk your biscuits in tea or mince-down tough meats. 
• Select easy and soft food like fish rather than meat, and cake rather than biscuit. 
• Chew food carefully and slowly, taking your time. 
• Consider having smaller meals often than larger meals  one time. Sip water in between to allow the food to wash down. You can also include nutritional supplements in your diet.

Here is a chart designed by the myotonic dystrophy foundation on the major food groups with examples of modified food.

Swallowing Techniques and Exercises

There are certain exercises that can help to strengthen the muscles and aid in swallowing. These exercises should be done after the consultation with the physician and should be repeated as many times as indicated by the physician.

• Effortful Swallow: Collect all saliva to the centre of the tongue and keep your lips closed and tight pretend that you are swallowing a grape. 
• Shaker exercise: Lie flat on your back and raise your head trying to fix your gaze at your toes. Make sure you don't move your shoulder while doing this.
• Jaw Thrust: Push the lower jaw as far forward as possible. Try to place the lower teeth in front of the upper teeth and hold this position.
• Masako Maneuver: Stick the tongue out of your mouth and bite down gently to keep it in place. Try to hold the tongue between the teeth and swallow. Release the tongue and repeat.
• Mendelsohn Maneuver: Locate the adam’s apple by pressing the index, middle and ring finger on your neck. Swallow once noticed the movement of Adam's apple. Swallow again while trying to squeeze the adam’s apple gently to hold it in its highest point. Hold for as long as indicated by your physician.

Medical and surgical interventions

Medications may be given to alleviate symptoms like the reflux of gastric acids and heartburn . For children and adults with severe problems who are unable to take medication and food through mouth, feeding tubes are recommended.

Summary

The dysphagia associated with myotonic dystrophy should be managed with care since it can be one of the most difficult complications. It not only leads to increased muscle weakness, but can also result in chest infections and aspiration of food. Early diagnosis and management of dysphagia is crucial as it may improve the overall quality of life of the patient. By modifying the diet and practising swallowing exercises, the dysphagia in myotonic dystrophy can be managed effectively. The patient should be encouraged to take food and medication by mouth as far as possible. With the help of appropriate consultants whenever necessary to manage the symptoms, maximum functional independence can be achieved and thus help the patient to regain their normal life.