Myopathy and Myasthenia Flashcards
What are the hereditary causes of muscle disease?
muscular dystrophies congenital myopathies myotonias channelopathies metabolic myopathies mitochnodrial myopathies
What are the acquired causes of muscle disease?
inflammatory/immune myopathies
myopathies associated with systemic illness
endocrine myopathies
drug induced/toxic myopathies
What is the most common pattern of myopathy?
proximal ‘limb girdle’ weakness
What is the classic pattern of fascioscapulohumeral muscular dystrophy?
proximal arm/distal leg (scalpuloperoneal) weakness
What is the classic pattern of inclusion body myositis?
distal arm/proximal leg weakness
What does weakness of flexion of the distal thumb (weakness of flexor pollicis longus) usually indicate?
inclusion body myositis
What are the causes of the pattern ptosis with or without ophthalmoplegia?
mitochondrial myopathies (CPEO)
oculopharyngeal muscular dystrophy
cranial neuropathies
myasthenia gravis
What investigations should be ordered to investigate myopathy?
CK, urine myoglobin EMG autoimmune tests muscle imaging muscle biopsy genetic testing
What is the difference between myotonia and paramyotonia?
myotonia improves with exercise
paramyotonia worsens with exercise
What is the commonest inherited neuromuscular disease in adults?
myotonic dystrophy type 1
What is the inheritance pattern of myotonic dystrophy type 1?
autosomal dominant
A mutation in which gene causes myotonic dystrophy type 1?
myotonin protein kinase (DMPK)
What type of mutation causes myotonic dystrophy type 1?
CTG repeat
What is the characteristic weakness of myotonic dystrophy type 1?
distal > proximal
What are the clinical features of myotonic dystrophy type 1?
myotonia weakness sternomastoid/temporalis wasting frontal balding diabetes/insulin resistance hypogonadal, hypopituitary cataracts intellectual impairment cardiac conduction defects cardiomyopathy respiratory and swallowing difficulties
What is the differential diagnosis for episodic recurrent weakness?
myasthenia
periodic paralysis
CIDP
porphyria
What is the differential diagnosis for episodic recurrent myalgia?
myositis
connective tissue disease
CIDP
metabolic defects
What is the differential diagnosis for recurrent rhabdomyolysis?
toxic
viral myositis
dystrophy
metabolic defects
What are the two types of metabolic myopathies?
lipid storage myopathy
glycogen storage myopathy
What type of exercise precipitates lipid storage myopathy?
prolonged moderate exercise
What type of exercise precipitates glycogen storage myopathy?
brief high intensity exercise
What is the commonest familial metabolic cause of rhabdomyolysis?
CPT II deficiency (lipid storage myopathy)
What are the treatment options for myasthenia gravis?
pyridostigmine corticosteroids IVIG PLEX oral immunosuppressants (e.g. azathioprine, mycophenolate)
Is rituximab used in myasthenia gravis?
treatment of choice for MuSK + MG (IgG4 disease)
sometimes used for AChR + MG
What is the mechanism of action of eculizumab?
complement inhibitor
What did the MGTX study show?
thymectomy is effective compared to pred alone for treatment of MG
Which patients have NT5C1a autoantibodies?
inclusion body myositis patients
Does stopping the statin treat anti-HMGCoA reductase myopathy?
no
Which particular antibodies are associated with cancer in dermatomyositis?
TIF gamma Ab
NXP2
anti p155
What is eteplirsen?
an oligomer which triggers excision of exon 51 during pre-mRNA splicing of the dystrophin RNA transcript - used to treat DMD
