Dystrophia Myotonica Flashcards
What are the clinical signs of dystrophia myotonica?
(See also dystrophia myotonica dance)
Gross appearance
1. Myopathic facies - long thin expressionless face, wasting of facial, temporalis, masseter, sternomastoid muscles
(Drooping mouth, drooping eyes, sleepy, frontal bald, expressionless guy)
2. Bilateral ptosis (can be unilateral) with difficult to open eyes after firm closure
3. Frontotemporal balding
4. Dysarthria (on speaking)
5. Walking aids, shoe/ankle/orthoses support for foot drop, shoes front scuffing
Limbs
5. Distal UL (hands) / LL (foot)
- Myotonia and percussion myotonia
- Distal wasting and weakness
- Impaired fine movements
6. Foot drop
7. Reduced or absent of deep tendon reflexes
8. High stepping gait (due to distal weakness)
Offer to examine
9. Cataracts (posterior subcapsular) - fundoscopy
10. Cardiovascular - cardiomyopathy, MVP, arrhythmia, AF (look for PPM)
11. Glucose monitoring - diabetes
12. Swallowing test - dysphagia
13. Sleep study - nocturnal hypoventilation with daytime somnolence
14. Hypogonadism - gynaecomastia, testicular atrophy
15. Goitre - nodular thyroid enlargement, thyroidectomy scars
Explain the genetics of dystonia myotonica
Autosomal dominant of trinucleotide repeat CTG expansion (up to 2000 times) in myotonin protein kinase gene
Genetic anticipation (earlier onset with generation) and expansion (severe onset with generation)
(Normal population: repeat of 5-36 times)
Two types:
- DM1: expansion of CTG trinucleotide repeat sequence in DMPK gene on chromosome 19
- DM2: expansion of CCTG tetranucleotide repeat sequence within ZNF9 gene on chromosome 3
(But type 2 is associated with proximal wasting and weakness)
How is dystonia myotonica diagnosed?
Clinical features
EEG: dive-bomber potentials
Genetic testing
How is dystrophia myotonica managed?
- Multidisciplinary team approach
- PT OT - Orthosis, lower limb support
- ST - swallowing defect
- Respi - CPAP for hypoventilation
- Phenytoin, quinine, procainamide may help myotonia (caution in conduction defect)
- Advise against general anaesthetic (high risk cardiac/respiratory complications)
Patients die prematurely of cardiac and respiratory complications
Weakness is a major problem
Look at this patient and examine as appropriate
Dystrophia myotonica dance
Often very vague examination instructions, examine as appropriate Look, feel, move Myotonic facies should give clear clue Look at walking aids and shoes prior to starting Go through CN examination - focus on wasting, myotonia, ptosis Go through distal parts of limbs - focus on reflexes, distal muscle wasting, weakness, myotonia Offer to examine other parts
- Head and face
- Drooping mouth, drooping eyes, sleepy, frontal bald, expressionless guy
- Careful: may be camouflaged by hair covering the frontal areas or wig
- Ptosis unilateral or bilateral
- Cataracts
- Ask to close eyes, don’t let you open - easily overcome eye closure, then difficult to open eyes
- Ask to whistle or blow candle
- Ask to clench teeth - palpate temporalis and masseter muscles
- Tongue myotonia
- Turn head to one side, palpate contralateral sternocleidomasoid muscle
- Hand over forehead, test neck flexion - Hands - distal wasting and weakness
- Wasting of small muscles of hands, dorsal guttering
- Hyperextension deformities at MCPJ, flexion deformities at IPJ
- Hypothenar eminence percussion causing dent that refills slowly (delayed relaxation)
- Clench fist and release - slow releasing grip (grip myotonia) - care: may be absent in late disease
- Absent of deep tendon reflexes - Feet
- Foot drop
- High stepping gait
- Walking aids, shoe/ankle/orthoses support for foot drop, shoes front scuffing - Offer to examine
- Cataracts (posterior subcapsular) - fundoscopy
- Cardiovascular - cardiomyopathy, MVP, arrhythmia, AF (look for PPM)
- Glucose monitoring - diabetes
- Swallowing test - dysphagia
- Sleep study - nocturnal hypoventilation with daytime somnolence
- Hypogonadism - gynaecomastia, testicular atrophy
- Goitre - nodular thyroid enlargement, thyroidectomy scars
What other conditions has trinucleotide repeat expansions?
- Dystrophia myotonica
- Fragile X syndrome
- Huntington’s chorea
- Friedreich’s ataxia
- Spinocerebellar ataxia
- Dentatorubropallidolysian atrophy
What are the cardiovascular complications of dystrophia myotonica? (4)
- Cardiomyopathy
- LVH
- Fibrofatty changes
- Myocardial myotonia - Conduction defects - 1st / 2nd / 3rd degree heart block
- Arrhythmias
- AF in 25%
- VT
- SVT (commonest) - Mitral valve prolapse
What are the endocrine complications of dystrophia myotonica? (3)
- DM
- Hypogonadism
- Nodular thyroid enlargement
What are the gastrointestinal complications of dystrophia myotonica? (6)
- Dysphagia
- Reflux
- Delayed gastric emptying, hypomotility
- Malabsorption
- Bacterial overgrowth
- Megacolon
What are the respiratory complications of dystrophia myotonica? (3)
- Weakness of respiratory muscles (hypoventilation)
- Respiratory failure following anaesthesia
- Recurrent pneumonia
What are the causes of myotonia?
- Dystrophia myotonica
- Myotonia congenita (Thomsen/Becker disease) - chloride ion channelopathy
- Paramyotonia congenita - sodium ion channelopathy
(precipitated by exertion, stress, cold, surprises, potassium rich food) - Hyperkalaemic periodic paralysis (HPP)
- Drugs - clofibrate
What are the causes of distal wasting and weakness? (5+4)
-> to move this card to different section
- Dystrophia myotonica
- Hereditary motor sensory neuropathy (HMSN)
- Distal spinal muscular atrophy
- Inclusion body myositis
- Oculopharyngodistal myopathy
Others
6. Welander distal myopathy
7. Finish distal myopathy
8. Markesbury distal myopathy
9. Miyoshi myopathy
What is myotonia?
Continued contraction of muscle after voluntary contraction ceases, with impaired relaxation
In what conditions can grip myotonia be absent?
- Late stage - severe wasting of small muscles
- Patient on pharmacotherapeutics - phenytoin
