Muscle in health and disease Flashcards
What are the 2 different types of congenital fibre type disproportion?
When type 1 (slow, aerobic) fibres are LARGE, type 2 (fast, anaerobic) are SMALL
When type 1 (slow, aerobic) fibres are SMALL, type 2 (fast, anaerobic) are NORMAL-LARGE
*both types are relatively mild –> not usually any long-term damage
- may fatigue more easily and become exercise resistant
type 1 - stain pale
type 2 - stain darker
What is the rate of muscle loss (sarcopenia) after age 50 years? how does this change if a person is physically inactive?
0.5-1% loss >50 years
3-5% if physically inactive
- no difference between men and women
(reduced muscle strength and balance = more prone to fractures)
What are the general symptoms and diagnosis of muscle disorders?
history:
- pain and weakness
- twitching and cramps
- muscle atrophy and contractures
- family history
- drug exposure
- endocrine disorders
diagnosis:
- biopsy
- EMG
Where is a muscle biopsy usually taken from and why?
usually taken from quadriceps (largest/one of largest muscle groups)
good indicator of damage
How could EMG be used to distinguish myopathy and neuropathy?
Myopathy: spontaneous active + constantly active
Neuropathy: silent areas with random bursts of activity
What are polymyositis and dermatomyositis? What are the typical clinical features?
Both are associated with microbial infection
Autoimmune (2:1 prevalence in females)
40-60 y/os
Clinical features:
- symmetrical involvement of large proximal muscles of shoulders, arms and thighs
- serum creatinine kinase elevated
- EMG (typical irritability in 90%)
- Biopsy - most definitive
- -> variation in fibre size
- -> central nuclei
- -> necrosis + regeneration (presence of macrophages)
- -> infiltrate of inflammatory cells (lymphocytes)
*dermatomyositis will also present with purplish rash and often has a streaky pattern
What antibody is associated with the most severe progression of subcutaneous calcifications?
Anti-Jo1
likely to have calcifications in muscle and skin (lymphocytes in epidermis)
How is subcutaneous calcification treated?
- corticosteroids
- high dose prednisone per day
- maintained until creatine kinase is normal (for 2 weeks) - azathioprine
- MTX
What is the prognosis for subcutaneous calcification?
5 year survival = 80%
8 year survival = 73%
Death from: malignancy, infection, pulmonary involvement
Increased risk of premature mortality if anti-Jo1 positive
What is inclusion body myositis?
Most common muscle disease of elderly (especially males)
muscle weakness:
- finger and wrists flexors more than extensors and shoulder abductors
- knee extensors more than hip flexors
- loss of quadriceps reflex and dysphagia
How is inclusion body myositis diagnosed?
Mild elevation in creatinine kinase
Biopsy: fibres contain empty vacuoles and clumps of cellular material –> contains amyloid material
- filamentous inclusions of IBM have optical properties of amyloid and contain beta amyloid, hyperphosphorylated tau and apoE, presenilin 1, prion protein and other proteins
Which types of muscular dystrophies are x-linked?
- Duchenne and becker MD
- Limb girdle MD
- Emery-Dreifuss MD
Which types of muscular dystrophies are autosomal dominant?
- Oculopharyngeal muscular dystrophy
- facioscapulohumeral muscular dystrophies
- limb girdle dystrophy
- emery dreifuss MD
Which types of muscular dystrophies are autosomal recessive?
- limb girdle dystrophy
2. emery dreifuss MD
What is dystrophin?
a cytoplasmic protein
it is shock absorbing
it connects the actin to the membrane and the dystrophin glycosylation complex (DGC)
DGC connects to/interacts with the ECM
