Muscle in Health and Disease

Question 1

What substance does muscle act as a store for?

Answer 1

Potassium

Question 2

What allows muscle cells to repair?

Answer 2

Presence of satellite cells

Question 3

What is a motor unit?

Answer 3

The group of muscles fibres that are innervated by a single motor neurone (5-200 fibres)

Question 4

What are myofibrils?

Answer 4

Multinucleate cells with nuclei at a peripheral location

Question 5

How does muscle appear histologically if there is loss of a single motor unit?

Answer 5

Fibres appear more angular and smaller (atrophy) due to loss of innervation

Question 6

What is the cause of infantile hypotonia?

Answer 6

A congenital fibre type disproportion where there is either larger type 1 fibres or smaller the 2 fibres

Question 7

What are the two fibre types present in muscle?

Answer 7

Type 1 fibres - stain paler and are slow twitch

Type 2 fibres - stain darker and are fast twitch

Question 8

What are polymyositis and dermatomyositis?

Answer 8

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.

Question 9

What are the clinical features of polymyositis and dermatomyositis?

Answer 9

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.

Question 10

How are polymyositis and dermatomyositis treated?

Answer 10

High-dose corticosteroids (e.g. prednisolone) given until creatine kinase is normal, and azathioprine and methotrexate may be used

Question 11

Describe the rash present in dermatomyositis

Answer 11

Typically purplish in colour and often has a streaky pattern; can also cause a rash over the eyelids with oedema

Question 12

Who is mainly affected by polymyositis and dermatomyositis?

Answer 12

40-60 year olds

Question 13

What is inclusion body myositis?

Answer 13

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

Question 14

What neurological condition is inclusion body myositis similar to?

Answer 14

Alzheimer’s disease due to presence of amyloid plaques, tau and ApoE

Question 15

What is the most common muscle disease of the elderly?

Answer 15

Inclusion body myositis

Question 16

What are the clinical features of inclusion body myositis?

Answer 16

• 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

Question 17

What would the biopsy findings be of inclusion body myositis?

Answer 17

Muscle fibres contain empty vacuoles and cellular material (beta amyloid, hyperphosphorylated tau, apolipoprotein E)

Question 18

What is duchenne muscular dystrophy?

Answer 18

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

Question 19

Why don’t girls (generally) get duchenne muscular dystrophy (DMD)

Answer 19

It’s an X linked condition, women have two copies so don’t tend to inherit two of the gene, functioning gene over-rides

Question 20

How does duchenne muscular dystrophy appear on biopsy?

Answer 20

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

Question 21

How can corticosteroids induce myopathies?

Answer 21

Can lead to type 2 (fast twitch) fibre atrophy

Question 22

How can statins induce myopathies?

Answer 22

Statins can lead to rhabdomyolysis (muscle fibre disintegrates/necrosis which can lead to kidney failure)

Question 23

How may chronic alcohol consumption lead to a myopathy?

Answer 23

Leads to slow progressive proximal weakness due to type 2 fibre atrophy

Question 24

How may acute/binge alcohol consumption lead to a myopathy?

Answer 24

Can lead to rhabdomyolysis

Question 25

What is fibromyalgia?

Answer 25

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.

Question 26

How is fibromyalgia treated?

Answer 26

Tricyclic antidepressants (amitriptyline), SSRIs (fluoxetine), exercise and complementary therapy

Question 27

How would a neuropathy appear on an EMG (electromyogram)?

Answer 27

Reduced fibrillation with greater downwards spikes

Question 28

How would a myopathy appear on an EMG (electromyogram)?

Answer 28

Rapid fibrillation