Look at this patient's face.
Examine this patient's cranial nerves.
· Onset usually in the third and fourth decade. However, if the mother is the carrier then the disease may manifest in infancy and
undergo rapid deterioration at the usual age of onset.
· Onset dominated by weakness or myotonia or both.
· Difficulty in releasing grip.
· Leg weakness (difficulty in kicking a ball).
· 'Pseudo-drop attacks' (due to weakness of quadriceps muscle).
· Ask the patient whether or not he has dysphagia (oesophageal involvement).
· Impotence (due to gonadal atrophy).
· Recurrent respiratory infections (due to weakness of muscles of bronchioles).
· While shaking hands with the patient, note the myotonia.
· Frontal baldness. (Note. The patient may be wearing a wig and it is important to mention that he is wearing one.)
· Ptosis (bilateral or unilateral) with a smooth forehead.
· Cataracts (posterior capsular cataracts) or evidence of surgery for cataracts.
· Difficulty in opening the eyes after firm closure.
· Expressionless face ('hatchet face') with wasting of temporalis, masseters and sternomastoids and 'swan neck' due to thinning
of the neck.
Proceed as follows:
-Distal muscles of the upper limbs, wasting, percussion myotonia over thenar
muscles and weakness.
- Deep tendon jerks (depressed).
· Tell the examiner that you would like to do the following: -Check the urine for sugar (diabetes mellitus). -Test higher intellectual
function (low IQ). -Examine for gynaecomastia and testicular atrophy.
This patient has frontal balding, myotonia, cataracts and wasting of the sternomastoids (lesion) due to dystrophia myotonica
(aetiology). He has dysphagia and severe muscular weakness (functional status).
What is the inheritance of this condition?
Autosomal dominant; the gene is located on chromosome 19q13.3. The condition usually presents in the third and fourth decades.
The disease tends to be worse in successive generations (known as anticipation). As a result the grandparent may merely have
cataracts while the grandchild develops a severe progressive form of the disease. Positional cloning has helped to identify the
myotonic dystrophy gene and localized a dynamic mutation with an increase in the number of trinucleotide repeats (AGC repeat).
The repeat size typically increases from generation to gener-ation, providing a molecular basis for the clinical phenomenon of
anticipation (Science 1992; 255:1253 5; Nature 1992; 355: 545-6; N Engl J Med 1993; 328:471 ).
What are the other features of this condition?
· Cardiomyopathy and cardiac conduction defects.
· Respiratory infection (low serum immunoglobulin G levels).
· External ophthalmoplegia (occasionally).
What do you understand by myotonia?
It is continued contraction of the muscle after voluntary contraction ceases, followed by impaired relaxation.
What therapeutic modalities are available?
Procainamide or phenytoin has been used in disabling myotonia. No treatment has
altered the course of progressive weakness.
What other forms of myotonia do you know?
Myotonia congenita or Oppenheim's disease, an autosomal dominant condition which presents at birth with feeding difficulties. The
myotonia improves with age and there is no dystrophy. Although this is considered to be a myopathy, changes have been reported
in the motor nuclei of the spinal cord and motor cortex.
In which myopathies is distal weakness prominent?
· Myotonic dystrophy.
· Welander's distal myopathy.
If this patient requires major surgery, what fact would you keep in mind?
Patients with dystrophia myotonica tend to do poorly alter the administration of general anaesthetic (due to impaired
cardiorespiratory malfunction) and will require intensive postoperative observation.
Mention some causes of bilateral ptosis.
· Myasthenia gravis. · Ocular myopathy.
· Congenital muscular dystrophies. · Syphilis.
What is the pathognomonic pattern of cataract in dystrophia myotonica ?
The patient's sister is worried about risks to her offspring. What tests would you perform?
· Clinical examination.
· Electromyography (EMG).
· Slit-lamp examination for cataracts.
Is prenatal diagnosis available?
Yes - in some families. The myotonic dystrophy gene is linked to the ABH secretor gene. However, not all families are informative.
What is the characteristic EMG finding?
Waxing and waning of the potentials, known as the dive-bomber effect. EMG changes are found in almost any muscle.
How would you manage such patients?
· Foot-drop is controlled by calipers or moulded-foot orthoses.
· Myotonia, when disabling, may respond to phenytoin (avoid quinidine and pro-cainamide as they can worsen cardiac
· Advanced heart block with or without syncope should be considered for pace-maker insertion.
Delege, in 1890, first described the association of myotonia with muscular atrophy.
Batten and Gibb (Brain 1909; 32: 187), and Steinert (Dtsch Z Nervenheilk 1909; 37: 58), in 1909 independently described the clinical
features of the symptom complex. Curschmann in 1912 emphasized the dystrophic symptoms and applied the term 'dystrophia