Myotonic dystrophy

The adult or classic form is the most common form of DM1. Adult DM1 is highly variable. It can differ in the way it presents, as well as in its severity between different individuals even within the same family. It is multi-systemic affecting different systems of the body. Not everyone will have all of these symptoms and they can change over time. The condition is degenerative, which means that it gets worse over time.

Progressive muscle weakness and fatigue are predominant features of the adult form of myotonic dystrophy. The first affected muscles are usually those in the face, eyelids, jaw and neck. In some cases, other muscles such as those in the hand may start to deteriorate first, causing difficulties when gripping or lifting objects (e.g. opening jars or lifting a glass). When weakness reaches the muscle around the ankles it will interfere with walking (foot drop) and can result in trips and falls. The muscles closer to the trunk of the body become weaker later. This causes difficulties when climbing stairs, getting up from a chair or from the floor (for example after a fall).

Fatigue and daytime sleepiness (or reduced energy during the day) are usually in the top three most predominant symptoms of the disease. These signs interfere significantly with performance in daily life and work or school activities. These signs can be dismissed without diagnosis, until more severe muscle issues appear. 

Patients will most likely recognise that something is not quite right when the first signs of “myotonia” appear. Myotonia is the inability to relax the muscle after a contraction (muscle stiffness that cannot be released). It usually affects the hands, and causes difficulties when releasing the grip. It can also affect the jaw and tongue, interfering with speech and swallowing. Myotonia is not necessarily one of the first signs of the disease, but is one of the first signs that triggers a referral for diagnosis, as it cannot be attributed to anything else.

The condition can vary between individuals and from day to day so patients may need to use walking aids or a wheelchair, especially when tired, but many adult patients with DM1 remain able to walk.

Adult Myotonic Dystrophy often affects the conduction system of the heart.  This can present with reduced heart rate (bradycardia). It can also manifest with dizziness or even short episodes of loss of consciousness (blackouts). Heart problems can affect life expectancy if they are not treated. 

Myotonic Dystrophy can also affect other types of body systems such as:

• Weakness in the respiratory muscles (required for breathing) can cause insufficient exchange of oxygen and carbon dioxide in the lungs (hypoventilation).
  • Hypoventilation might first manifest at night and cause symptoms such as tiredness in the morning, poor appetite and loss of weight, morning headaches.
  • The weakness of the respiratory muscles can also increase the risk of sleep apnoea (holding the breath when sleeping). 
  • It can also increase the risk of chest infections and cause breathing difficulties during infections.
  • If patients develop hypoventilation or sleep apnoea, they might be prescribed with a ventilator (BiPAP or CPAP) to support their breathing during the night. 
• Weakness can also affect the muscles present in the throat and oesophagus. This results in difficulty swallowing and increased risk of choking and aspiration (breathing in food or liquids).
• The bowel is often affected. This causes symptoms like those experienced by people with irritable bowel syndrome, including irregular bowel movements with either diarrhoea or constipation. Bowel symptoms can be severe enough to affect daily life.
• Early-onset cataracts are common in adults with myotonic dystrophy.
• Premature balding is common in men with the disease.
• Cognitive disorders are common in DM1. The severity and the impact on daily life can vary from one person to another. Cognitive involvement can manifest with:
  • Learning difficulties
  • Reduced attention span
  • Depression or reduced motivation
  • Difficulties with planning or executive function
  • Anxiety
  • Apathetic temperament 
  • Obsessive or avoiding personality trait
  • Autistic like behaviours
• Adults with myotonic dystrophy have a higher risk of developing diabetes type 2. 
• Changes in hormone production can result in disturbed menstrual cycles for women. They can also result in low libidos for men.
• It affects the endocrine system, resulting in thyroid problems. 
• There is some evidence suggesting a higher risk of a certain type of cancers (like thyroid, ovarian, testicular and skin melanoma). Close monitoring is recommended.