Overview

When it comes to muscle weakness, you may have heard of the medical term muscular dystrophy, but what exactly is it, and are there variations to the area affected and the degree of severity? Muscular dystrophy is a type of hereditary disease that causes muscle weakness and loss of muscle mass. 

Myotonic dystrophy is the most common type of muscle dystrophy seen in adults, which affects the smaller muscles first, in the face, jaw, and neck.¹ Intricate systems can be affected by this disease, including: 

• The conductivity of the heart
• Breathing and swallowing muscles
• Bowels and the lens of the eyes² resulting in cataracts.

These symptoms are debilitating, therefore it is important to address them so it doesn’t affect the ability to perform daily tasks. Exercising is a great way to reduce muscle weakness and aid rehabilitation, and physiotherapists can help improve your muscle strength and flexibility. 

Types of myotonic dystrophy

To understand how to treat myotonic dystrophy, one needs to understand that there are two types of myotonic dystrophy, DM1 and DM2. These types of myotonic dystrophy vary in severity. The area of muscle weakness also differs between the two types, as distal muscles are affected in DM1, but the proximal muscles are affected in DM2.

Distal muscles are the muscles farthest from the centre of the body. This includes the forearms and intrinsic muscles of the hands and ankles. The muscles that are used for picking up your foot when walking may also weaken due to this condition, which might cause someone to trip and fall. Proximal muscles are muscles that are closer to the centre of the body. Individuals with DM2 tend to have a weak thigh, hip flexor, and extension muscles. 

DM1 is the most common type of myotonic dystrophy and is more severe compared to DM2.Muscle weakness can occur even to the most essential muscles associated with breathing and swallowing (dysphagia). Respiratory muscle weakness is not a common feature of DM2, but it is exhibited in individuals with DM1. The functionality of the lungs progressively declines³ and this also may cause sleep apnoea.

People with DM1 or DM2 are also more prone to getting cataracts, which refers to when the lens of the eye becomes cloudy, interfering with vision. In people with either type of myotonic dystrophy, cataracts appear earlier, around the age of 40.

Mild forms of DM1 are characterised by mild muscle weakness, delayed relaxation of muscles, and cataracts. It usually occurs in people between the ages of 20-70, and life expectancy is normal³ for both mild forms of DM1 and people who have DM2. However, people who have myotonic dystrophy as children or teenagers may have a shorter life expectancy.²

Diagnosis

To diagnose myotonic dystrophy, a healthcare professional will conduct a physical examination and may ask questions about:

• Personal medical history
• Family medical history, especially if there is any history of relatives with DM
• Presenting symptoms

Symptoms

Symptoms include:

• Myotonia - sustained muscle contractions that can manifest as the inability to release a tightened fist quickly
• Muscle weakness
• Cataracts - where the lens in the eyes become clouded
• Excessive sleep or sleepiness
• Dysphagia - issues with swallowing
• Behavioural and learning difficulties in children
• Slow and irregular heartbeat

Myotonic dystrophy can also cause diabetes-like symptoms, such as insulin resistance.⁴ This refers to a condition in which the body requires more insulin than normal to function properly, eventually becoming insensitive to insulin. 

Insulin isn't the only hormone affected by this disease. There have also been reports of endocrine abnormalities increasing among people with DM1 over time, specifically involving thyroid problems.⁵

Patients with DM1 in particular, often develop hypothyroidism, a condition by which the thyroid is not creating and releasing enough thyroid hormone into the bloodstream.

Cause

Myotonic dystrophy is a dominant inherited muscular dystrophy caused by an abnormal expansion of DNA sequences within certain genes, which results in issues with muscle function. Being a dominant disease means that someone only needs to inherit this gene from one parent for them to be affected. In DM1, there is an unusual increase of the DNA base CTG repeats in the Dystrophia Myotonica Protein Kinase gene (DMPK) on chromosome 19. Normally the DMPK is responsible for maintaining muscle health and function.⁶

In DM2, a different DNA sequence is affected, causing an abnormal increase of the CCTG bases on the Cellular Nucleic Binding Protein (CNBP) gene on chromosome 3. The CNBP functions to regulate activity of other genes through activation and deactivation, but it is also essential for development.²

To successfully diagnose myotonic dystrophy (DM1 or DM2), a history and physical examination are taken first. As this disease is caused by an abnormality in specific genes (DMPK and CNBP), a genetics test is also conducted with a blood sample to obtain a definite diagnosis.⁷

Since myotonic dystrophy affects and shifts the cardiac conduction of the heart, an electrocardiography (ECG) is used to monitor the heart for any irregularity.⁷ To further test the other muscles besides the heart, an electromyogram (EMG) may be used. 

Treatment

Because myotonic dystrophy affects different muscles around the body, specific treatments are used depending on symptoms and area affected. For example, if you have muscle weakness, mexiletine helps with muscle stiffness.² Since there is currently still no known cure to this disease, the only way to treat it involves mitigating and reducing the adverse effects of the disease.

Benefits of exercise

Exercise can help reduce the severity of myotonic dystrophy and improve functionality of muscles by strengthening the muscles. Here are a few different types of exercise that can help:

Aerobic exercise

Aerobic exercise can help to increase the maximum oxygen uptake in individuals with DM1,⁸ as it involves an increase inheart rate and respiratory rate. The recommended duration of moderate-to-intense activity should be around 2.5 hours per week.⁹ It may sound daunting but this doesn’t have to be an intensive exercise, and it can be spread throughout a series of days. Activities include brisk walking or jogging, swimming, water aerobics, dancing, or doing chores around the house such as vacuuming.¹⁰

It can be tricky to perform aerobic exercises with myotonic dystrophy due to a difficulty with balance and ankle weakness. In this case, using gym equipment would be ideal, as it can safely secure your feet whilst exercising. This includes elliptical machines or an exercise bike. Cycling alone can result in improved muscle function in sedentary people with myotonic dystrophy Type 1, including cardiorespiratory fitness, muscular endurance, and mobility.¹¹

Strength and Resistance training

Loss of strength can be slowed down by exercising because physical training increases the size of the muscle fibres. Resistance training may also help with myotonic dystrophy, as well as increasing your strength and endurance.

Strength exercises that you can do include:

• Light dumbbells or weight machines
• Resistance bands

Balance training

Balance training involves a mixture of exercises that strengthen your muscles, to support your body and prevent you from falling. By strengthening your core, bottom and legs, it will help with your stability and balance.

Stretching

Another great exercise is stretching, as it can reduce the tightness in muscles, increase flexibility, and allow further range of motion over time. An increase in joint flexibility may also help reduce the risk of tripping over when walking. It is beneficial to hold a stretch for at least 60 seconds or perform sets of two 30 second stretches. This could be achieved through stretching exercises or yoga. Because it is quick to do and it is low intensity, it can easily fit into someone’s daily schedule.

Myotonic dystrophy can also have an impact on your mental health. Exercising is known to help to improve your mood and energy levels as it triggers the release of the “feel good” hormone endorphins.

Although exercising can help with reducing the severity of the disease, there are challenges you may face when trying to exercise. For instance, managing fatigue and staying motivated can be tricky when trying to maintain consistency. By implementing small intervals of exercise a day at the start can help you ease into a workout routine and help with setting up goals to achieve. Safety concerns are to be considered as well, it is best to look out for any signs of overexertion or dehydration and to rest properly to avoid injuries.

Before working out with myotonic dystrophy, make sure you speak to your healthcare professional to develop workout plans that are suitable for your needs. 

Summary

In general, exercise is important for maintaining a healthy body, but it can also help strengthen your muscles and increase your flexibility. As respiratory failure and heart abnormalities are the main causes of poor prognosis with this condition, exercising could help enhance your cardiovascular and respiratory health. Incorporating exercise into your routine could help reduce and manage the symptoms associated with myotonic dystrophy, ultimately improving your quality of life.