Muscles of movement
There are two problems that may affect muscles of movement or ‘skeletal muscle’.
The first is a gradual weakening of certain muscles, over time, caused by a ‘muscular dystrophy’. The muscles in the face, eyelids, jaw and neck are commonly affected. The muscles in the forearm that enable us to grip objects are often affected early on. The muscles around the ankles are also commonly affected, causing ’foot drop’, which cause people to catch their toes and trip. The large, weight-bearing muscles of the legs and thighs are usually affected much later.
The rate of deterioration in muscle strength is typically slow over many years. Some people never have significant muscle weakness. Some people, who are more severely affected, may need a wheelchair, but many people with myotonic dystrophy do not.
The second problem affecting skeletal muscles is an electrical problem, called ‘myotonia’. Myotonia causes muscle stiffness (difficulty relaxing the muscle), which especially affects the hands and jaw. This can be helped with medication supplied by your specialist but usually does not need treatment.
Heart
The wiring or ‘conduction system’ of the heart is often affected and this can lead to attacks of dizziness or even blackouts. Sometimes a pacemaker or other device may be recommended. The mechanical system which pumps the heart may be affected but usually it does not cause a problem that needs treatment.
Lungs
The pumping of air in and out of the lungs, or ‘ventilation’, may be affected. This may cause daytime sleepiness and increase the risk of chest infections, especially after a general anaesthetic. Pneumonia is very common and requires prompt treatment. You should stay up-to-date with your immunisations, including the flu and pneumococcal vaccines.
Gastrointestinal (GI) tract
Because the swallowing muscles are affected, swallowing can often lead to coughing and spluttering when eating or drinking. This can be dangerous. If food or drink goes into the lungs rather than the stomach, this leads to ‘aspiration pneumonia’, which is a severe chest infection. The lower bowels are also typically affected by irritable bowel syndromelike symptoms, with a mixture of constipation, crampy abdominal pain and diarrhoea.
Lens of the eye
It is very common for cataracts to form across the lens of the eye in people with myotonic dystrophy, but they usually cause few symptoms because they appear so slowly. However, early onset cataracts can be easily treated.
Brain
The brain can be affected in many ways and excessive daytime sleepiness is one of the most common consequences. Reduced motivation can also be a common problem.
Children with myotonic dystrophy may have learning difficulties, even if they have no muscle problems.
Myotonic dystrophy type 2 (DM2)
An important recent advance is the recognition of a second, milder condition with features resembling myotonic dystrophy type 1 (DM1). In this condition, weakness tends to occur in muscles close to joints (proximal muscles), such as those in the neck, fingers, elbows and hips. Facial weakness and myotonia (difficulty relaxing the muscle) is often mild or absent. Cataracts and heart problems can occur but are usually less severe than in DM1.