AWABS - Myopathies Flashcards
Classification of myopathies
Primary
Secondary
Primary myopathies
Muscular (muscular dystrophy)
Congenital
Metabolic
Acquired myopathies
Metabolic and endocrine
Dermato- and poly- myositis
Drug induced
Infectious
?Polymyalgia ?Fibromyalgia
Metabolic myopathies
Glycogen storage
Lipid storage
Muscular dystrophy features
Involves dystrophin
Inherited
Progressive
Muscular dystrophy synptoms
Inability to regenerate
Proximal weakness
Respiratory involvement eventually
Myotonia
Types of muscular dystrophy
Dystrophia myotonica
Becker’s
Thomsen’s
Duschenne’s muscular / myotonic dystrophy
Congenital myopathy features
Rare
Genetic defects lead to protein defects
Non progressive
Reduced contractile ability
Metabolic myopathy features
Hereditary enzyme defects
Errors in metabolism of ATP
Examples of glycogen storage diseases
Pompe’s disease
McArdle’s disease
Enzyme affected in Pompe’s disease
Acid maltase
Enzyme affected in McArdle disease
Myophosphorylase
Examples of lipid storage diseases
Carnitine palmitoyltransferase deficiency
Myopathic carnitine deficiency
Examples of acquired metabolic and endocrine myopathies
Thyroid disease
Parathyroid disease
Pituitary disease eg Addison’s
Corticosteroids eg Cushing’s
Diabetes
Acquired infectious causes of myopathy
Trichinosis
Toxoplasmosis
HIV
Coxsackie
Lyme disease
Influenza
Acquired drug induced causes of myopathy
Statins
Steroids
Alcohol
Cocaine
Colchicine
Most common form of myopathy
Drug induced
Incidence of Duchenne’s muscular dystrophy
1:4000 in boys
Features of Duchenne’s
Progressive muscular wasting
Poor balance
Drooping eyelids
Atrophy
Scoliosis
Waddling gait
Cardiomyopathy
Genetics of Duchenne’s
X linked recessive
Mutation on dystrophin gene at locus Xp21
Ix for Duchenne’s
Raised CK
EMG
Genetic testing
Muscle biopsy
Rx of Duchenne’s
High dose steroids
Ataluren
Exercise / Physio
Role of steroids in Duchenne’s
Increase muscle strength
Reduce Symptoms
Prolong life
Dystrophin features
Large cytosolic protein
Hydrophobic
Rod shaped
Connects cytoskeleton to extracellular matrix
Becker’s dystrophy genetics
Same as Duchenne’s
Features of Becker’s
More rare than Duchenne’s
Later onset (teens)
Milder
Normal life expectancy
Dilated cardiomyopathy
Features of dystrophia myotonica (myotonic dystrophy)
Inherited
Slow progressing
Difficulty initiating movement
Cataracts
Cardiac conduction defects
Categories of Dystrophia myotonica
DM1
DM2
Features of DM1
Steinert disease
Severe congenital
Childhood
Features of DM2
Proximal myotonic myopathy
Adult onset
Rare
Genetics of dystrophia myotonica
Autosomal dominant
Features of acid maltase deficiency
Resp failure
Pulmonary HTN
Cardiomegaly
Aspiration risk
Lipid storage myopathy features
Hypoglycaemia
Acidosis
Rhabdomyolysis
Cardiac failure
Management of lipid storage myopathies in perioperative period
Require administration of supportive substrates
Implication of mitochondrial myopathies for anaesthetics
Worsened by depressant anaesthetics
Maintain normoglycaemia
Avoid suxamethonium
Sensitive to non depolarising NMB so give 10-20% dose
Risk of heart block and seizures
Risk of rhabdo with volatiles - ?use TIVA
Features of peripheral neuropathy to distinguish from myopathy
Distal muscles affected
Fasciculations
Somatosensory abnormalities
Reduced reflexes
