Myotonic Dystrophy : Causes, Symptoms, Diagnosis, Treatment, Prognosis, and Recovery

Myotonic dystrophy is an inherited and complex condition characterized by progressive muscle atrophy and weakness.^{(1, 2)} Individuals suffering from this condition commonly suffer from persistent contractions of the muscles, which are known as myotonia, and are unable to relax certain muscles after using them.⁽¹⁾

There are many symptoms of Myotonic Dystrophy (DM) and this condition affects various body systems, such as: eyes, heart muscles, skeletal muscles, cardiovascular system, central nervous system and endocrine system.

There are two primary types of myotonic dystrophy:⁽¹⁾

Myotonic dystrophy type 1 (DM1), also referred to as Steinert disease⁽⁴⁾ and this type has four subtypes: classic, mild, congenital and childhood.

Myotonic dystrophy type 2 (DM2), which is also referred to as proximal myotonic myopathy.

The symptoms of both the types of myotonic dystrophy can overlap; however, the type 2 is milder than the type 1 myotonic dystrophy.^{(1, 4)}

Muscular dystrophy is a group comprising of more than 30 genetic conditions which results in muscle weakness and causes a kind of myopathy, which is a condition affecting the skeletal muscles. As time goes, there is shrinking and weakness of the muscles causing difficulty in walking and doing daily activities, which can in turn affect the lungs and heart.

Myotonic dystrophy is a common type of muscular dystrophy, which starts in adulthood. However, there are certain forms of myotonic dystrophy which can also develop in infancy or childhood.

There are different types of myotonic dystrophy which start at different ages:

Classic myotonic dystrophy type 1 often develops in the 20s, 30s or 40s.

Mild myotonic dystrophy type 1 affects individuals aged 20 to 70 years old.

Congenital myotonic dystrophy type 1 affects infants and is present from birth itself.

Childhood myotonic dystrophy type 1 develops commonly around the age of 10.

Myotonic dystrophy type 2 usually starts in adulthood with the average age of onset being 48 years.

Myotonic dystrophy affects a minimum of 1 in 8,000 people all over the world. The prevalence of this condition varies according to geographic and ethnic population. This condition is the commonest muscular dystrophy in people of European ancestry.^{(2, 4)} Type 1 is more common in most populations than type 2.

The primary symptoms of myotonic dystrophy, which worsen with time are: muscle weakness, muscle wasting and myotonia.⁽⁴⁾

Myotonia is where a person is not able to relax their muscles voluntarily, such as a person suffering from this condition will not be able to let go of something after holding it.⁽⁴⁾

However, myotonic dystrophy affects different parts of the body, which leads to development of various symptoms. The type of myotonic dystrophy determines the severity and the speed at which the symptoms develop and progress.

The symptoms of this type develop in adulthood with the primary symptoms being myotonia. This is more obvious after a period of rest and it gets better with muscle activity. Other symptoms consist of :^{(2, 4)}

• Wasting of facial muscles leads to a myopathic face, which is a thin and sharp face.
• Distal muscle weakness is where the muscles situated farthest from the center of the body get affected and this causes difficulty with fine motor tasks which you do using your hands and foot drop, which leads to an impaired gait.
• Heart conduction abnormalities are also seen.

The signs of congenital myotonic dystrophy which can be seen before birth are:^{(2, 4)}

• Polyhydramnios, where there is excessive amniotic fluid present.
• Reduction in the fetal movements.
• Clubfoot seen in the fetus.
• Ventriculomegaly is also seen in the fetus.

• Intellectual disability.
• Weak facial muscles cause a tented appearance of the upper lip.
• Slurred speech.
• Hypotonia, which is decreased muscle tone.

Symptoms of mild myotonic dystrophy type 1 often start to develop between the ages of 20 and 70 years and consist of⁽⁴⁾ cataracts, myotonia and mild weakness of the muscle.

The symptoms often start to develop around the age 10 and consist of:⁽²⁾

• Slurred speech.
• Psychosocial problems and learning difficulties.
• Heart conduction abnormalities.
• Hand muscle myotonia.

These symptoms often start to develop in adulthood and can be different from patient to patient. Symptoms of myotonic dystrophy type 2 consist of:^{(2, 4)}

• Stiffness or weakness of the proximal muscles.
• Myofascial pain.
• Varying grip myotonia.
• Early-onset cataracts that is developing before the age of 50.
• Loss of hearing.
• Pain is one of the main complaints seen in myotonic dystrophy type 2. The patient describes it as musculoskeletal, abdominal and exercise-related pain.

Myotonic dystrophy is genetic and this condition is passed from the parent to their child.⁽¹⁾ The cause of this condition is thought to be changes in the DMPK gene which lead to development of myotonic dystrophy type 1; and alterations in the CNBP gene lead to development of myotonic dystrophy type 2.⁽¹⁾

Identical changes in the structure of the CNBP and DMPK genes cause myotonic dystrophy type 1 and type 2. Both the times, a part of the DNA gets repeated abnormally multiple times leading to formation of an unstable portion in the gene.⁽²⁾ The severity of the symptoms of myotonic dystrophy is directly proportional to the number of times the DNA gets abnormally repeated.

According to scientific evidence, the excess messenger RNA produced due to the abnormal DNA repetition is harmful and causes disturbance with the production of the cell proteins. This in turn leads to signs and symptoms in different organs in myotonic dystrophy.

Diagnosis of myotonic dystrophy is made by your doctor by conducting a physical exam and asking questions about: symptoms, personal medical history and family medical history.

There are some medical tests which help in confirming the diagnosis of myotonic dystrophy. Genetic testing can be done for confirming the diagnosis of myotonic dystrophy.⁽²⁾ This test looks for mutations in the affected genes.

For further confirmation of the diagnosis, the following tests are done :⁽²⁾

Creatine Kinase Blood Test: Creatine kinase is an enzyme which is primarily found in the heart and skeletal muscle. The cells present in the heart or skeletal muscles discharge creatine kinase into the blood upon any damage. In patients with mild myotonic dystrophy, this test can be slightly elevated but is normal mostly.

Electromyogram (EMG): In this test electrical activity of the muscle fibers is assessed with the help of a fine needle electrode, which is inserted into the muscles. Usually, people having myotonic dystrophy have extreme waxing and waning of the electrical activity in their muscles when at rest.

Muscle Biopsy: In this test, a small sample of cells and tissue is taken from the muscles and sent to the lab for analysis. Other tests done for checking the function of certain organs affected by myotonic dystrophy are:

Electrocardiogram is done to check the function of the heart.

Sleep study is done to look for hypersomnia and obstructive sleep apnea.

Pulmonary function testing is done to check for neuromuscular respiratory failure.

Myotonic dystrophy has no cure as of now.^{(2, 3)} Treatment is done for managing the patient’s symptoms and improving and increasing the quality of life and independence of the patient.^{(2, 3)} Different parts of the body can be affected by myotonic dystrophy and treatment depends on the symptoms and consists of:

• Medications which reduce sustained myotonia, such as sodium channel blockers tricyclic antidepressants, calcium antagonists or benzodiazepines.
• Neurostimulants are prescribed to deal with excessive daytime sleepiness.
• A CPAP machine is used for managing sleep apnea.
• Cataract surgery is done for removing the cataracts and improving the vision.
• Synthetic testosterone is given for treating male hypogonadism.
• Treatment for diabetes is done with medications in pill form or insulin can also be used. Myotonic dystrophy increases the risk of diabetes from insulin resistance.
• Occupational and physical therapy are one of the vital parts of treatment for increasing independence for individuals suffering from myotonic dystrophy. It helps in strengthening the muscles and in learning new methods of doing daily tasks.
• Other than this, assistive devices like canes, braces and wheelchair are beneficial in decreasing the dependency of the patient on other people.
• Speech-language pathologist helps patients who are experiencing difficulty with slurred speech and swallowing.

Seeing that this is an inherited condition, there is no way to prevent this condition except choosing not to have any biological kids. Seek genetic counseling before trying for a biological child to talk about the risk of passing myotonic dystrophy or other genetic conditions to your child.

The prognosis of myotonic dystrophy depends on its type and the age of the patient when is starts. Poor prognosis and decreased life expectancy is associated with earlier age of symptom onset.^{(2, 3)} About half of the patients suffering from type 1 myotonic dystrophy need a wheelchair for moving around before death. Patients having type 2 myotonic dystrophy have milder symptoms and usually do not need assistive devices for moving around.

The type of myotonic dystrophy determines the average life expectancy.

The neonatal mortality rate is about 18% for infants having congenital myotonic dystrophy.⁽⁴⁾ Around 25% of patients with congenital myotonic dystrophy die before reaching the age of 18 months and half of them die before reaching their mid-30s.

Patients with mild myotonic dystrophy often have normal life spans. The lifespan is decreased when compared to the average in classic myotonic dystrophy.

Myotonic dystrophy is a disorder, which affects multiple systems of the body and hence needs a multi-disciplinary approach, consisting of effective rehabilitation programs which help in maintaining the quality of life of the patient and also to increase the patient’s psychosocial and physical functions. A good rehabilitation program also helps in reducing any secondary medical co-morbidity and also to prevent or decrease physical deformities so the patient can live as much a normal life as possible. There has been good development of customized rehabilitative programs for recovery of motor function in different patients suffering from different neurological conditions. Neuro-modulation approaches and physical therapy helps in restricting the left over plasticity of the brain for increasing the functional recovery of the patients and help in recovery.

This is why understanding cortical plasticity in patients suffering from DM1 is beneficial in developing a personalized rehabilitative program, which also limits the plasticity which encourages motor recovery, helped by neuro-modulation strategies. There is also some research on the central nervous system in defined myopathies which also includes myotonic dystrophy.

Myotonic dystrophy is a potentially fatal condition. The type of myotonic dystrophy determines the age when the patient dies. Neuromuscular-associated respiratory failure is the leading cause of death in myotonic dystrophy, followed by cardiovascular complications.

References:

Also Read:

• Understanding Myotonic Dystrophy : Causes, Types, Symptoms, and Treatment