THE DIFFERENT TYPES OF MYOTONIC DYSTROPHY
Summary of the lecture by Christine E.M. De Die- Smulders MD of the University of Maastricht at the yearly meeting organised in October 1996 by the “Werkgroep Dystrophia Myotonica” for patients and other people involved in myotonic dystrophy. This lecture was meant for the new participants of this annual meeting.
Myotonic Dystrophy (DM) is a relatively frequently occurring, hereditary muscular disorder. Characteristic symptoms are myotonia (muscle stiffness due to muscles failing to relax properly) and slowly progressive muscle weakness, especially of the face-muscles, the throat- and neck-muscles and the muscles in the fore-arm and lower part of the legs. Other organs may also be affected. This manifests itself in symptoms as cataract, irregular heart-beat, slowness, loss of initiative and infertility in males. There may be a considerable variation in the severeness among patients. The age at onset of the disorder and the character of the symptoms are highly depending upon the length of the expansion of the CTG repeat in the DM-gene.
Classification in four types according to age and main symptoms
1 Mild type
2 Adult (= classic) type
3 Childhood type
4 Congenital type
Adult type (2)
Age at onset: 12 – 50 years
Increasing muscle weakness
Slowness, loss of initiative
Defects in several organs
The adult (classic) type is the most frequently occurring type. Myotonia and muscle weakness develop from puberty till the age of 50. Myotonia is a painless muscle stiffness, notably affecting the hands after a firm grip. Complaints are: difficulties with letting loose a door-handle and after shaking hands or cramp when wringing out a cloth, especially in wintertime. The stiffness disappears spontaneously after a short time. Cold can evoke or stimulate this stiffness. Most patients are slightly troubled by myotonia and will not complain spontaneously about it.
The muscle weakness starts gradually and it may last for years before a patient consults a doctor. Weakness of face-muscles appears at an early stage: The eyelids hang down and when the patient is asleep part of the white of the eye stays visible. It is no longer possible to laugh broadly. Speech gets indistinct and it looks like the patient speaks “through his nose”. The temples shrink by the jaw-muscles getting thinner. The weakness of the bending muscles of the neck is often pronounced. Patients cannot raise their heads when lying down. The loss of power in the muscles of the fore-arm and hands makes together with the myotonia the hands clumsy. Regarding the muscles the lower part of the legs especially the raising of the feet is reduced: The patients start shuffling, stumble over minor roughness’ and fall more frequently. Sometimes next to these there are less specific complaints such as fatigue, lack of spirit, stomach-complaints or swallowing problems.
In a later stage of the disease the muscle weakness will increase and the muscles of the upper-arm and upper-part of the leg will be affected. Most patients however stay mobile if their radius of action is reduced till in and around their homes. Seldomly patients get bound to a wheelchair.
Mild type (1)
Age at onset: over 50 years
The mild type starts after the age of 50. Most patients only get cataract. In a later stage mild muscle weakness and myotonia may appear. If the illness is unknown in the family it is seldom recognised that the cataract is part of a muscle-disease.
Congenital type (4)
Much amniotic fluid
Reduced fetal movements
Problems with breathing and swallowing
First year of life:
Muscle weakness decreases
Baby learns breathing and drinking by him/herself
After the first year of life:
Learn to walk (2 – 5 years of age)
Learn to speak (sometimes indistinctly)
Problems with learning
Inflammation of the ears
Problems with bowels
The congenital type shows severe muscle weakness and decreased muscle strength at birth which leads to problems with breathing and swallowing. During pregnancy there is much amniotic fluid (because the baby does not swallow) and the mother feels less stirring of the baby. A number of babies die because of breathing problems. If they survive they recover considerably from the muscle weakness during the first years of life, because of growth of the muscles. Indeed these children often have the characteristic tent-shaped mouth. The patients show a retarded motor development, which needs treatment by a physiotherapist. A majority of the children learns to walk between the age of 2 and 5 years. Bowel cramping and constipation often occur, just like inflammation of the inner ears. Besides there are problems with speaking, among others due to weakness of the palate. At adult age muscle stiffness and muscle weakness occur.
The mental retardation with this type is often mild to moderate. The children learn to speak and learn to take care of themselves, but mostly they do not learn to read and write. It is important to test the child in time and to choose the right type of school based on the testresults. Most children need special education. Take care that the child is not underestimated. Factors which may influence underestimation are the facial muscle weakness, the problems with speaking, poor hearing and slowness.
The congenital type is almost always passed on by an affected mother, seldom by an affected father.