Muscle in Health and Disease Flashcards
What substance does muscle act as a store for?
Potassium
What allows muscle cells to repair?
Presence of satellite cells
What is a motor unit?
The group of muscles fibres that are innervated by a single motor neurone (5-200 fibres)
What are myofibrils?
Multinucleate cells with nuclei at a peripheral location
How does muscle appear histologically if there is loss of a single motor unit?
Fibres appear more angular and smaller (atrophy) due to loss of innervation
What is the cause of infantile hypotonia?
A congenital fibre type disproportion where there is either larger type 1 fibres or smaller the 2 fibres
What are the two fibre types present in muscle?
Type 1 fibres - stain paler and are slow twitch
Type 2 fibres - stain darker and are fast twitch
What are polymyositis and dermatomyositis?
This is associated with a microbial infection which leads to an autoimmune response. Lymphocytes come in from the blood supply around the fascicles and therefore the perimysium is targeted first.
What are the clinical features of polymyositis and dermatomyositis?
Elevated serum creatine kinase (muscle damage), symmetrical involvement of large proximal muscles (shoulder, arms, thighs), biopsy shows varying fibre size, central nuclei, necrosis and regeneration with lymphocytic infiltration.
How are polymyositis and dermatomyositis treated?
High-dose corticosteroids (e.g. prednisolone) given until creatine kinase is normal, and azathioprine and methotrexate may be used
Describe the rash present in dermatomyositis
Typically purplish in colour and often has a streaky pattern; can also cause a rash over the eyelids with oedema
Who is mainly affected by polymyositis and dermatomyositis?
40-60 year olds
What is inclusion body myositis?
An inflammatory muscle disease characterized by slowly progressive weakness and wasting of both distal and proximal muscles, most apparent in the muscles of the arms and legs
What neurological condition is inclusion body myositis similar to?
Alzheimer’s disease due to presence of amyloid plaques, tau and ApoE
What is the most common muscle disease of the elderly?
Inclusion body myositis
What are the clinical features of inclusion body myositis?
- Mild elevation in creatine kinase
- Muscle weakness – finger and wrist flexors are weaker than the extensors and shoulder abductor, and knee extensors are weaker than the hip flexors.
- Dysphagia
- Associated polyneuropathy
- Loss of quadriceps reflex
What would the biopsy findings be of inclusion body myositis?
Muscle fibres contain empty vacuoles and cellular material (beta amyloid, hyperphosphorylated tau, apolipoprotein E)
What is duchenne muscular dystrophy?
An X-linked condition that leads to proximal muscle weakness in the first two years of life followed by a slow decline in mobility followed by death in their early 30s
Why don’t girls (generally) get duchenne muscular dystrophy (DMD)
It’s an X linked condition, women have two copies so don’t tend to inherit two of the gene, functioning gene over-rides
How does duchenne muscular dystrophy appear on biopsy?
Variable muscle fibre size, fibrosis of the endomysium and degeneration of muscle fibres (myophagocytosis) with replacement with fibrotic material and fat (leading to muscle weakness).
Will also have elevated creatine kinase as a result
How can corticosteroids induce myopathies?
Can lead to type 2 (fast twitch) fibre atrophy
How can statins induce myopathies?
Statins can lead to rhabdomyolysis (muscle fibre disintegrates/necrosis which can lead to kidney failure)
How may chronic alcohol consumption lead to a myopathy?
Leads to slow progressive proximal weakness due to type 2 fibre atrophy
How may acute/binge alcohol consumption lead to a myopathy?
Can lead to rhabdomyolysis
What is fibromyalgia?
Where there is widespread muscle pain that affects both sides of the body above and below the waist. It is associated with fatigue and sleep disturbance and mainly affects 3-60 year-old females.
How is fibromyalgia treated?
Tricyclic antidepressants (amitriptyline), SSRIs (fluoxetine), exercise and complementary therapy
How would a neuropathy appear on an EMG (electromyogram)?
Reduced fibrillation with greater downwards spikes
How would a myopathy appear on an EMG (electromyogram)?
Rapid fibrillation
