Dystrophia Myotonica
Approach to Congenital Myopathies
1. Duchenne’s, Becker’s
2. Myotonia
 Dystrophia myotonica (fascioscapular dystrophies can mimic appearance)
 Congenital myotonia
 Hereditary paramyotonia
3. Fascioscapulahumeral dystrophies, limb-girdle dystrophies, distal myopathies
Examination
Examine patient’s face or hands (Can be short case of locomotor or in CNS station)
Examine the hands
 Demonstrate difficulty opening hands after shaking
 Repeatedly open and close the hands
 Percussion myotonia of the thenar eminence
 (proceed with hand examination with function assessment if locomotor station)
 Demonstrate weakness in the forearms (especially) and hands
 No sensory loss
 Loss of reflexes
 Check the pulse (dysrhythmias, small volume pulse)
Examine the face
 Myopathic facies
 Expressionless
 Triangular facies
 Wasting of the temporalis, masseter (palpate these muscles when patient clenches
teeth)
 Frontal balding
 Bilateral ptosis
 Close his eyes and open
 Tongue for percussion myotonia
 Gum hypertrophy from phenytoin toxicity
 Swan-neck appearance with wasting of the SCM (test for weakness of SCM),
weakness of flexion of the neck
 Nodular thyroid enlargement
Request
 Face
 Cataracts - posterior subcapsular and stellate
 Assess Speech – slurring due to myotonia of the tongue and pharyngeal
muscle
 Chest examination
 Gynecomastia
 Cardiovascular examination – dilated cardiomyopathy (split S1, mitral
murmur, low BP and pulse volume)
 Testicular atrophy
 Urine dipstick for diabetes mellitus
 Lower limbs – bilateral footdrop
Presentation
Sir, this patient has got dystrophia myotonica as evidenced by
 A myopathic facies that is triangular in appearance with an expressionless look.
There is wasting of the facial muscles involving the temporalis and masseter
muscles associated with frontal balding and bilateral ptosis. He had difficulty
opening his eyes after firm closure. There was myotonia affecting the tongue.
 There is also a swan-neck appearance with wasting of the sternocleidomastoid
muscles with weakness of flexion of the neck. On shaking his hand, there was a
delay in releasing his grip. In addition, after making a fist, he was unable to
quickly open it especially after doing this repetitively. There was also presence of
percussion myotonia of the thenar eminence. There is presence of proximal
myopathy and wasting with involvement of the forearms and hands. There are
also reduced reflexes with no sensory loss detected. Function is relatively
preserved.
 With regards to complications
 His pulse is regular at 80 bpm with a small volume pulse suggesting dil CMP
 There was no gum hypertrophy to suggest chronic phenytoin use.
 There is nodular thyroid enlargement.
 I would like to complete my examination by
 Face
 Cataracts - posterior subcapsular and stellate
 Assess Speech – slurring due to myotonia of the tongue and pharyngeal
muscle
 Chest examination
 Gynecomastia
 Cardiovascular examination – dilated cardiomyopathy (split S1, mitral
murmur, low BP and pulse volume)
 Testicular atrophy
 Urine dipstick for diabetes mellitus
 Lower limbs – foot drop with high steppage gait (tibial nerves are affected
early)
Questions
What are the types of muscular dystrophies you know of?
1. Duchenne’s
 Sex linked
 Pseudohypertrophy of the calves or deltoids
 Gower’s sign, proximal weakness
 Cardiomyopathy
Becker’s
 Sex linked
 Later onset and less severe form of Duchenne’s
2. Limb-girdle
 Autosomal recessive
 Shoulder and pelvic girdle affected
 Third decade
 Sparing of the face and heart
Fascioscapulohumeral
 Autosomal dominant
 Bilateral, symmetrical weakness of the facial and SCM with bilateral ptosis
 Weakness of the shoulder muscles and later the pelvic girdle muscles
3. Dystrophia myotonica
Congenital myotonia
Hereditary paramyotonia
4. Distal myopathies eg Welander’s myopathy
What is myotonia?
Continued contraction of the muscles after voluntary contraction ceases,
followed by impaired relaxation.
What is dystrophia myotonica?
 Characteristic clinical appearance with myotonia and weakness with no sensory
loss
 Autosomal dominant with a trinucleotide (AGC) repeat disorder on chromosome
19
 Anticipation – phenotypic expression worsens with each successive generation
 Onset in the 3rd or 4th decade
 Males>females
 In addition to the characteristic facies and musculoskeletal involvement
 Intellectual and personality disorder
 Cataracts – posterior subcapsular cataracts which are stellate type
 CVM – dilated cardiomyopathy and conduction defects
 Resp – recurrent infection from weakness of the bronchiolar musculature,
hypoventilation and post-anaesthetic respiratory failure
 Abdomen – dysmotility and dysphagia
 Testicular atrophy and gynecomastia
 Diabetes mellitus
 Nodular thyroid enlargement
How would you investigate?
 Confirm Diagnosis
 EMG – dive bomber pattern ie waxing and waning of the potentials
 Muscle biopsy shows no inflammatory changes with type 1 fibre atrophy
which is characteristic but not diagnostic
 DNA analysis
 Muscle enzymes are normal
 Screen for Complications
 FPG – screen for diabetes mellitus
 ECG – heart blocks, small P, prolonged PR, notched QRS and prolonged QTc
 CXR – enlarged heart
 Slit-lamp examination for cataracts
How would you manage?
 Education, genetic counselling
 PT/OT – eg foot orthosis for foot drop
 Medications – phenytoin for myotonia, other anti-myotonic medications such as
quinine and procainamide should be avoided due to aggravation of cardiac
conduction defects; however it is the weakness that causes disability and not
myotonia
 Pacemaker for 3rd degree heart block or symptomatic such as syncope
How would you counsel the patient’s family?
 Vertical
 Autosomal dominant, children 1 in 2
 Anticipation
 DNA analysis is available for some families for prenatal diagnosis
 Horizontal
 Screen with clinical examination
 Slit-lamp examination
 EMG
What are the other types of myotonia disorders?
 Myotonia congenita (Oppenheim’s disease)
 Autosomal dominant or recessive
 Presence of myotonia without other features of dystrophia myotonica
 Present at infancy with difficulty feeding with subsequent improvement
 No weakness and reflexes are preserved
 Herculean appearance
 Channelopathies
 Hereditary paramyotonia
 Autosomal dominant
 Cold-induced myotonia
What are your differential diagnoses for dystrophia myotonica?
 Facies appearance – Facioscapulohumeral dystrophy
 Autosomal dominant, onset at age 10-40, Chr4, normal lifespan
 Face – ptosis, difficulty closing eyes, facial weakness and speech impaired
 Normal IQ
 Neck – wasted SCM and weakness
 Shoulder – winging of scapula, weakness of pectoralis, trapezius, biceps and
triceps and hypertrophy of deltoids
 Occasionally affecting the anterior tibialis
 Normal CK
 Proximal weakness – FSH, limb-girdle, prox myopathy causes, MG
 Limb Girdle dystrophy (see prox myopathy)
 Distal weakness – Welander’s distal myopathy, nerve problem
 Myotonia – Congenital myotonia, hereditary paramyotonia