Muscle in Health and Disease Flashcards
What is the role of muscle?
- 40% body mass
- 80% water
- store for intracellular ions
- important for heat production
What are the properties of skeletal muscle?
- actin and myosin sarcomere bands causing contraction
- individual cells fuse into multinucleated fibres
- linked to motor neurons
- many form a motor unit contracting together
- satellite cells
What are satellite cells?
- repair cells
- take up central location in damaged cells
- as they mature and repair muscle they are pushed peripherally so centre becomes full of contractile proteins
What happens if an axon is damaged?
- in periphery/spinal cord
- muscle fibres of motor unit become inactive
- undergo atrophy = small angulated muscle fibres
- sprouting of neighbouring motor neuron axons synapse with denervated fibres
- motor units enlarge and appear as groups
- if these neurons die = group atrophy
What is infantile hypotonia?
- floppy baby syndrome
- low muscle tone
- myopathic cause = most fibres small and few massive hypertrophic fibres
What are the 2 types of congenital fibre disproportion?
1) large type 1 muscle fibres paler and small type 2 muscle fibres darker
2) small type 1 paler and large type 2 muscle fibres darker
(slow type 1 aerobic metabolism and fast type 2 mixed aerobic and anaerobic)
What is sarcopenia?
- age related
- 0.5-1% muscle mass per year after 50
- no difference for men and women
- if physically inactive more muscle mass loss
What are the general symptoms of muscle disorders?
- pain and weakness
- twitching and cramps
- muscle atrophy and contractures
- family history
- drug use/exposure
- endocrine disorders
How are muscle disorders diagnosed?
- biopsy(gold standard, variation in fibre size, necrosis, infiltrate of inflammatory cells)
- EMG (fibrillation potential and positive waves when muscles at rest = damage, release of calcium from nearby damaged muscles causing neighbouring to contract)
What are the common inflammatory myopathies?
- polymyositis
- dermatomyositis
- both the same and only difference is can get rash with dermatomyositis (purple, streaky)
- autoimmune
- proximal muscle weakness
- associated with microbial infection
- starts at periphery of fascicle
- macrophages infiltrate into muscle
- weakening of large proximal muscles of shoulders/arm/thigh
- elevated creatine kinase
What is the significance of subcutaneous calcifications?
- in muscles and skin
- inflammatory myopathy sign
- anti-nuclear antibody positive -> anti-jo` antibody
What is the treatment for inflammatory myopathy?
- corticosteroids
- high dose of prednisolone per day
- maintain until creatine kinase normal
- also azathioprine and methotrexate
What is the prognosis of inflammatory myopathy?
- death from malignancy, infection, pulmonary involvement
- more likely death if anti-jo 1 positive
What is inclusion body myositis?
- most common muscle disease of elderly
- attacks particular set of muscles
- finger flexors and shoulder abductors
- knee extensors (quads)
- poor prognosis
- mild creatine kinase elevation
- polyneuropathy
- dysphagia as affects oesophagus skeletal muscle at top 1/3
What does a biopsy for inclusion body myositis show?
- empty vacuoles
- cellular material clumps
- filamentous inclusions containing presenelin 1, apolipoprotein E, hyperphosphorylated tau, amyloid like material
What are the X linked muscular dystrophies?
- Duchenne and becker muscular dystrophies
- limb girdle muscular dystrophy
- emery-dreifuss muscular dystrophy
What are the autosomal recessive muscular dystrophies?
- limb girdle muscular dystrophy
- emery dreifuss muscular dystrophy
What are the autosomal dominant muscular dystrophies?
- facioscapulohumeral muscular dystrophy
- oculopharyngela muscular dystrophy
- limb girdle muscular dystrophy
- emery dreifuss muscular dystrophy
What are Duchenne MD?
- dystrophin deficiency
- proximal muscle weakness during first 2 years
- continuous slow decline = death mid 20s/30s, elevated creatine kinase, unable to walk by 7-12 years
What is dystrophin?
- shock absorber to prevent damage
- muscle tears itself apart if not present
What are the early Duchenne MD biopsy signs?
- fibre size variability
- endomysial fibrosis
- degenerating muscle fibres undergoing myophagocytosis
What are the late Duchenne MD biopsy signs?
- later loss of muscle
- replaced with fibrotic material and fat
What are the 3 drug induced myopathies?
- corticosteroids = type 2 fibre atrophy
- statins = rhabdomyolysis
- alcohol = chronic = slow progressive proximal weakness
What is fibromyalgia?
- widespread muscle pain
- both sides of body above and below waist
- 11/18 specific tender points
- most positive for anti-polymer antibodies
- associated fatigue and sleep disturbance
- 30-60 year olds
- mostly females
- get poor sleep but need to cope with stress/pain so vicious cycle
What are the treatments for fibromyalgia?
- TCAs = amitryptilline
- SSRIs = fluoxetine
- exercise as complementary therapy
