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
What limbs are affected in the different types of MD?
- Duchenne + Becker MD: shoulders, chest, arms, hips, knees and legs
- Limb girdle: shoulders, chest, arms, hips, knees, legs
- Facioscapulohumeral: shoulders, legs/knees, face
- Emery-Dreifuss: shoulder, legs/knees
What is the main difference between Duchenne and Beckers MD?
Duchenne = complete loss of dystrophin Beckers = dystrophin is shortened
What changes occur to the muscle in Duchenne MD?
Fibre size variability
Endomysial fibrosis
Degenerating muscle fibres undergo myophagocytosis
Lost muscle is replaced with fat and fibrotic material
How is Duchenne MD currently treated/managed?
Corticosteroids
What is fibromyalgia? What are the treatment options?
Widespread muscle pain (cause cannot be found)
50% of pts are antipolymer antibodies positive
treat with tricyclic antidepressants (amitriptyline), SSRIs (fluoxetine), exercise, complementary therapy
