Introduction

Myotonic dystrophy (DM) is a genetic disorder that causes progressive muscle weakness. A major feature is the hyperexcitability of skeletal muscle (myotonia) whereby there is a delay in muscle relaxation after a forceful contraction of the muscle, which leads to cramping, stiffness or aching in the affected muscles. Depending on which muscle is affected and the severity of the disease, some symptoms include impaired ambulation, difficulty in releasing their grip, impaired neck function, reduced dexterity, and abnormal chewing. In addition, myotonic dystrophy has multisystem manifestations affecting the brain, cardiopulmonary, smooth muscle, gastrointestinal, liver, immune, and endocrine systems – leading to various disorders including cholelithiasis, insulin resistance, cardiac conduction defects, cataracts, respiratory problems, cognitive dysfunction and more.^1,2 

There are two types of myotonic dystrophy:

• Type 1 myotonic dystrophy (DM1), also known as ‘Steinert’s disease’
• Type 2 myotonic dystrophy (DM2), also known as proximal myotonic myopathy

DM1 is more common and tends to be more severe than DM2. Besides differences in point of mutations, the age of onset and occurrence of childhood cases also differ between the two types. There are no early childhood forms of DM2, hence DM2 is usually diagnosed at a later age compared to DM1. In addition, the pattern of muscle weakness also differs slightly, where DM2 has greater proximal muscle weakness than distal weakness in DM1. Both DM1 and DM2 are autosomal dominant forms of inheritance, in that it only takes a faulty gene from either parent to cause the symptoms.^3,4 

Currently, there is no cure for myotonic dystrophy. Therefore, the management of myotonic dystrophy relies on symptomatic treatment, genetic counselling, and continuous monitoring of disease progression. As symptoms and disease progression vary greatly among patients, coupled with the varying multisystem manifestations, a multidisciplinary approach is often required to provide optimal management. The treatment of myotonic dystrophy focuses on preserving functionality and independence, whilst preventing further complications.⁵ 

Organ-specific symptomatic treatment

Treatment of skeletal muscle problems

Myotonia is a common and frequent symptom presented in this group of patients. Depending on the degree of severity, some require an anti-myotonic agent, such as mexiletine, to manage myotonia. Mexiletine has been found to improve patients’ hand strength, eye and hand opening and muscle stiffness.^6,7 Patients may also benefit from physical and occupational therapy to improve movement, mobility, balance and functionality of the diseased muscles.

To improve muscle strength, low to moderate-intensity exercises are recommended. Patients who have impaired ambulation may require mobility aids, like a cane, walker or other assistive devices that would allow them to perform their daily activities. Besides that, pain management is an important part of treatment, as the aching of the limbs can be disruptive. Examples of pain medications that can be used in these patients are non-steroidal anti-inflammatory drugs (NSAIDs) or antidepressants.^8,9

Management of cardiac problems

Cardiac abnormalities in DM1 and DM2 are life-threatening, and account for 30% of fatalities in DM1.¹⁰ Common cardiac abnormalities associated with myotonic dystrophy are arrhythmias and conduction system defects. Prompt treatment is required when these abnormalities are detected to prevent sudden cardiac death. Cardiac pacemakers are usually recommended for high-risk patients, especially those with family history and symptoms suggestive of arrhythmias.

In some cases, an implantable defibrillator is used. Some cardiac medications like beta-blockers and anti-arrhythmic are used to manage the symptoms of heart failure. For both symptomatic and asymptomatic patients, a routine cardiac evaluation, such as electrocardiogram (ECG) and Holter monitor, are advised. A more frequent follow-up is required for patients who are at risk of major cardiac events which could result in sudden death.^11,12,13

Management of respiratory problems

Respiratory failure is the leading cause of death in DM1 patients. Respiratory dysfunction is common in myotonic dystrophy and is commonly associated with alveolar hypoventilation, hypercapnia, and sleep disturbance in the form of sleep apnoea. Symptoms arising from respiratory dysfunction, such as extreme daytime sleepiness and fatigue, have a negative impact on the patient’s quality of life. Treatments are available for sleep disorders, such as continuous positive airway pressure (CPAP) for sleep apnoea, non-invasive ventilation (NIV) for hypercapnia patients, and medication like modafinil is beneficial for patients who have extreme daytime sleepiness with no other associated sleep disorders. Invasive ventilation such as tracheostomy may be considered for patients with chronic respiratory dysfunction who do not respond to the above treatments, although it comes with serious complications.^14,15,16

Treatment of gastrointestinal problems

Gastrointestinal dysmotility may be a disability in some patients with myotonic dystrophy. Common complaints by patients are heartburn, regurgitation, difficulty in swallowing (dysphagia), indigestion (dyspepsia), bloating, abdominal pain and changes in bowel habits. Medications are usually prescribed to treat motility problems, such as laxatives, prokinetic and indigestion tablets. Patients are also advised to make dietary changes to prevent or ease the symptoms. For example, avoiding late-night meals may be beneficial for patients who have heartburn and bloating symptoms, and small, low-fat meals are recommended for patients who have bowel issues - either constipation or diarrhoea.

However, treatment can get complicated for patients who have difficulty swallowing, as it can lead to various medical complications such as respiratory and nutritional problems. The use of a hot pack, and exercising the muscles around the mouth area prior to eating, is helpful in coping with the symptom.^17,18

Management of endocrine problems

Some of the common endocrine problems associated with myotonic dystrophy are diabetes, thyroid dysfunction and androgen insufficiency. Thyroid dysfunction such as hyperparathyroidism can affect calcium metabolism, in which high calcium levels in the body can lead to complications like osteoporosis, kidney stones, and stomach ulcers if left untreated. Other thyroid dysfunction reported are either hypothyroidism or hyperthyroidism. Hormone replacement therapy is provided as required for these patients. Patients with diabetes would require insulin or oral anti-diabetic medication, depending on the severity of the condition. Necessary lifestyle modifications such as exercise and dietary adjustments are advised. As hormones are dysregulated in myotonic dystonic patients, they are at an increased risk for cancers like prostate, ovarian, breast and thyroid cancers, when compared to the general population.^19,20

Management of eye problems

Cataracts have been known to be associated with myotonic dystrophy. Cataracts can form early in DM, and it can negatively impact the patient’s daily life. Cataracts can significantly worsen a patient’s balance, which is already impaired due to muscle weakness. In addition, patients who have impaired ambulation are prone to falls if the cataracts are left undiagnosed and untreated. Cataract removal, which involves surgery, is often recommended if vision is severely impaired. Prompt referral to ophthalmologists, as soon as eye-related symptoms are reported, is crucial in myotonic dystrophy patients to prevent total loss of vision and optimal care of the eyes. Serial monitoring of cataracts is required for all myotonic dystrophy patients.^21,22

Genetic counselling and family planning

Since myotonic dystrophy is a hereditary disease, genetic testing is highly recommended, particularly when there is a known family history. It is the only definitive diagnosis method to date. Prior to genetic testing, both symptomatic or asymptomatic patients are referred to genetic counselling, where they will be provided with knowledge of the disease and the importance as well as the implication of the genetic testing. Genetic counselling is necessary and essential for patients who have children or plans to have children.

Patients should be made aware that the disease is highly likely to be inherited in children even if they are asymptomatic, and that the congenital onset of the disease is the most severe form. Intense prenatal counselling is recommended for pregnant or female patients who are trying to conceive. Although prenatal testing is available to perform prior to implantation or in-utero, patients should be made aware of the risks that come with pregnancy – a higher risk of ectopic pregnancy, miscarriage, stillbirth, placenta previa and premature labour associated with the disease, compared with the general population.^23,24,25

Summary

Myotonic dystrophy is a multisystem disorder that is mainly characterised by progressive muscle weakness. There are genetically two distinct types of myotonic dystrophy, which are type 1 and type 2. Type 1 myotonic dystrophy (DM1) is more common and is usually more severe than type 2 (DM2). A cure is currently non-existent for this disease, there are various treatment and management options available that are individualised depending on the patient’s condition. Although these treatments do not affect the disease outcome, they provide significant improvements in the well-being of patients. In addition to the symptomatic treatment and management, genetic counselling is equally important to provide mental support to the patients.