MYOTONIC DYSTROPHY

Introduction

Myotonic dystrophy, also known as Steinerts’s disease, it is the most frequently diagnosed adult form of muscular dystrophy. It is characterized primarily by progressive muscle weakness and muscle wasting and by myotonia (difficulty in relaxing a muscle or a group of muscles following contraction). It is a multisystem disease, typically involving a wide range of other tissues as well as muscles.

Causes & Risk Factors

Genetic: Myotonic dystrophy is a hereditary disorder transmitted from generation to generation by a parent who has the disorder. Myotonic dystrophy can affect either males or females. Approximately one person in 8,000 around the world is affected by myotonic dystrophy, but it occurs more frequently in some populations than in other. For example, in northern Quebec the incidence of myotonic dystrophy is exceptionally high, with up to one person in 500 being affected.

Age: Myotonic dystrophy can occur at any age, though a high percentage of affected people are diagnosed by their early twenties. An unusual feature of myotonic dystrophy is known as anticipation. Anticipation refers to the tendency for myotonic dystrophy to become more severe and the age at which symptoms appear to occur earlier as it passes down the generations of a family. Congenital myotonic dystrophy is the most severe form of myotonic dystrophy. Symptoms of this form of myotonic dystrophy are always evident at birth. In fact, decreased movements may be noted in the unborn child as early as the second trimester of pregnancy. Virtually all infants with congenital myotonic dystrophy are born to mothers who also have myotonic dystrophy. Myotonic dystrophy is not contagious.

Classification & Types

There are forms of myotonic dystrophy. They are the adult form and the congenital form.

Adult Form:

• This form generally becomes apparent when a person is between 10 and 30 years old. But in some cases, symptoms may appear in younger children or much later in life.
• The course of myotonic dystrophy varies widely form one person to the next, even among members of the same family. Some people with the disorder have such mild symptoms that they do not suspect anything wrong and adapt very easily. Others may be faced with a significant level of disability, requiring assistance with mobility and activities of daily living.
• In the adult form of myotonic dystrophy, muscle weakness usually starts gradually and progresses slowly. People with this form often mention stiffness as an early symptom. Disability typically occurs 15 to 20 years after the onset of the disease when the weakness affects the shoulder muscles, thighs and hips, though many people with myotonic dystrophy live their entire lives without any detectable symptoms.

Congenital form:

• The congenital form of myotonic dystrophy, as its name implies, is always present at birth. Affected infants are profoundly weak and have many difficulties. Frequently, there are problems associated with breathing, sucking and feeding.
• The babies are extremely hypotonic (decreased muscle tone) at birth, and as a result they appear floppy. Some babies die within a few hours or days of birth.
• Infants with congenital myotonic dystrophy have weakness in virtually all muscles, including the respiratory and facial muscles. If the infant survives the newborn period, a gradual improvement is generally noted in his/her respiratory function and ability to swallow. As they grow older, children are slow in developing language, making it difficult or impossible for them to live totally independent lives as adults.

Treatment Options

• At the present time, there is no cure or treatment available that can prevent or delay the progression of muscle weakness caused by myotonic dystrophy.
• Staying as active as possible remains the most effective way of maintaining the best physical condition. Rehabilitation specialists (physiotherapist and occupational therapists) can advise individuals affected by myotonic dystrophy and their families on how to create a stimulating environment. Also, they can prescribe an exercise program and aids that can assist an individual to carry out activities of daily living.
• There are medications available that can decrease the effects of myotonia, but they sometimes cause undesirable side effects. Drugs are usually prescribed only when myotonia prevents a person from working or performing daily activities.
• When necessary, surgery is available to clients who have cataracts. The operation, that may require a short stay in hospital, can result in substantially improved vision.
• Speech therapy can provide assistance to a child or adult who has difficulty speaking. An adapted educational environment can promote the development of a child’s abilities within school setting.
• Arrhythmias, dizziness and other symptoms associated with heart problems may be treated with medication when they are causing difficulties.
• If cold lasts for more than two weeks, treatment may be indicated. As well, some people may find it useful to be vaccinated against the flu.

Digestive problems may be decreased by attention to healthy eating habits. Some general suggestions include:

• Eating three meals a day at regular hours.
• Drinking plenty of liquids such as water, fruit juice and milk).
• Eating fiber-rich foods such as whole grain cereals, vegetables and fruit.
• Avoiding very cold foods such as ice cream and iced drinks.
• Chewing food slowly and well.

• A family will be seen by their own family-doctor and possibly, other health professionals. If necessary, they will be referred to a neuromuscular clinic as near to their home as possible.
• Treatment, if any, will vary according to the severity of weakness and the related problems that a person is experiencing. Because the course of myotonic dystrophy is so variable, even among members of the same family, it is difficult to be specific about who will need to be consulted. The following information is intended to serve as a guide to medical professionals with whom you may be in contact.
• The physician (PT) will teach chest physiotherapy techniques to children and adults that will enhance their physical wellness. The physiotherapist helps clients develop individual exercise programs to maintain optimum muscle strength. This program will include the amount of activity that is best for each person. The PT may also be consulted should respiratory difficulties occur.
• The geneticist will help individuals and their families to understand how this disorder has been transmitted within their family, as well as the impact of myotonic dystrophy on future generations.
• The occupational therapist (OT) can help clients learn how to adapt to physical limitation. The OT will be involved, as required, in choosing equipment and to enhance function at school or in the workplace.
• In conjunction with an infant development worker, the OT/PT may have suggestions for activities to stimulate intellectual development of babies and children with myotonic dystrophy.
• The role of the nurse, whether in the clinic or the community, is to work with the family to understand the disorder and its management.
• The social worker, in conjunction with the nurse, provides support to the individual and family member coping with the effects of myotonic dystrophy.

Diagnosis

• A diagnosis of myotonic dystrophy is made by a physician. A physical examination and a complete history are necessary for a doctor to assess the presence of myotonia, muscle weakness and any decrease in muscle size. Details of a positive family history, if present, will be investigated, as well as the history of the client’s present concerns.
• Diagnostic tests are also used by the physician in making a positive diagnosis of myotonic dystrophy.
• DNA Analysis performed on a sample of blood is a valuablediagnostic tool. This genetic test is used to make the diagnosis of myotonicdystrophy more exact. It identifies the presence or absence of the geneticfault that is responsible for myotonic dystrophy. Where there is a positivefamily history, the use of this test during pregnancy can also determinewhether or not a fetus is affected by myotonic dystrophy.
• An electromyogram (EMG),a test designed to measure and record electrical activity in muscles, is usefulin diagnosing many disorders affecting muscle. Electrodes are attached to thebody in a painless procedure. Accurate descriptions of muscle activity provideevidence of the presence or absence of myotonic dystrophy.
• A muscle biopsy is necessarywhenever a physician wants to clarify the diagnosis. A sample muscle tissue isexamined under a microscope for changes characteristic of myotonic dystrophy.
• An eye examination can identifythe opacities seen in the lens of a person who has cataracts. The presence ofcataracts may be the first or in some cases, the only symptoms seen in a personwith myotonic dystrophy. This information is important for diagnosis as well asfor management.