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Neurology > Disorders of muscle > Flashcards

Disorders of muscle Flashcards

1
Q

What are fasciculations?

A

Visible, fast, fine, spontaneous muscle twitches

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2
Q

What are some causes of fasciculations?

A

Physiological - Stress, caffeine, fatigue
Denervated muscle due to hyper excitability
Motor neurone disease

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3
Q

What is myotonia?

A

Failure of a muscle to relax after use
(Locking, sticking or cramping of the muscle)

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4
Q

What are some causes of myotonia?

A

Chloride and sodium channelopathies

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5
Q

What are some things examined for in muscle examination?

A

Inspection
Palpation
Strength testing
Fatiguability

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6
Q

How is muscle strength graded?

A

MRC muscle power grading:

  • 0 – no movement at all
  • 1 - flicker of movement when attempting to contract muscle
  • 2 – some muscle movement if gravity removed but none against gravity
  • 3 - movement against gravity but not against resistance
  • 4 – movement against resistance but not full strength
  • 5 – normal strength
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7
Q

What are some inflammatory myopathies?

A

Polymyositis
Dermatomyositis
Inclusion body myositis

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8
Q

What is polymyositis?

A

Idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness

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9
Q

What is dermatomyositis?

A

Clinically similar to polymyositis but also has typical cutaneous manifestations

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10
Q

Describe the aetiology of polymyositis and dermatomyositis

A
  • Idiopathic, autoimmune
  • Higher prevalence in females (2:1)
  • Peak incidence age 40-50
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11
Q

Describe the pathophysiology of dermatomyositis and polymyositis

A
  • T cell mediated process against (unidentified) muscle antigens
  • CD8+ T cells and macrophages surround, invade and destroy healthy, non-nectrotic muscle fibres
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12
Q

What are some symptoms of polymyositis?

A
  • Symmetrical, proximal muscle weakness in the upper and lower extremities
    • Insidious onset, worsening over months
    • Often specific problems e.g. difficulty brushing hair, climbing stairs
  • Myalgia in 25-50% (usually mild)
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13
Q

What are some signs of polymyositis?

A
  • Muscle wasting
  • Confrontational testing - direct testing of power
  • Isotonic testing - 30 second sit to stand
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14
Q

What are some skin symptoms of dermatomyositis?

A

Gottron’s sign
Shawl sign
Heliotrope rash

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15
Q

What is shown?

A

Gottron’s sign

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16
Q

What is shown?

A

Shawl sign

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17
Q

What is shown?

A

Heliotrope rash

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18
Q

What are some lung symptoms of polymyositis?

A
  • Interstitial lung disease (10% of patients, especially those positive for anti-Jo-1 antibody)
  • Respiratory muscle weakness
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19
Q

What are some oesophageal symptoms of polymyositis?

A

Dysphagia (Poor prognostic sign)

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20
Q

What are some cardiac symptoms of polymyositis?

A

Myocarditis

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21
Q

What are some systemic features of polymyositis?

A

Fever
Weight loss
Raynaud’s phenomenon
Inflammatory arthritis

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22
Q

What are some investigations required in polymyositis

A

Bloods
Electromyography (EMG)
MRI
Muscle biopsy

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23
Q

What bloods are required in polymyositis?

A

CK
Inflammatory markers
Electrolytes, Calcium, PTH, TSH
Autoantibodies

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24
Q

What are some autoantibodies found in polymyositis?

A

Non-specific = ANA, anti-RNP
Specific = Anti-Jo-1, anti-SRP

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25
Q

What will show on MRI in polymyositis?

A

Show signal intensity abnormalities due to muscle inflammation, oedema, fibrosis and calcification

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26
Q

What will muscle biopsy show in polymyositis?

A

Perivascular inflammation and muscle necrosis

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27
Q

What is 1st line treatment of polymyositis?

A

Prednisolone (Reducing dose)

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28
Q

What are some 2nd line treatments of polymyositis?

A
  1. Immunosuppression - azathioprine/methotrexate/ciclosporin
  2. IV Ig
  3. Biological therapy e.g. rituximab (B cell depleting therapy)
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29
Q

What are some possible complications of polymyositis?

A

Increased risk of malignancy (Especially in males over 45)

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30
Q

What are some cancers that have an increased risk in polymyositis?

A

Ovarian, breast, stomach, lung bladder and colon cancers

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31
Q

What is inclusion body myositis?

A

Idiopathic inflammatory myopathy usually occurring in men over 50 years

32
Q

How does inclusion body myositis present?

A
  • Slowly progressive weakness of mainly distal muscles
  • Characteristic thumb sparing
  • Weakness of the pharyngeal muscles causes difficulty in swallowing in over 50%
33
Q

What are some investigations required in inclusion body myositis?

A
  • CK - only slightly elevated
  • EMG - myopathic and neuropathic changes
  • MRI - changes often more distal but similar to polymyositis
  • Muscle biopsy
34
Q

How is inclusion body myositis managed?

A

Prednisolone

35
Q

What are muscular dystrophies?

A

A group of 9 progressive, inherited abnormalities of genes involved in normal muscle function, causing weakness and muscle degeneration

36
Q

What are some viral triggers of muscular dystrophy?

A
  • Coxsacchie virus
  • Trypanosomiasis
  • Cisticercosis - Undercooked pork (Pork tape worm)
  • Borrelia (E.g. Bergdorferi - Lyme’s disease)
37
Q

What are some toxic triggers of muscular dystrophies?

A

Drugs
Venom

38
Q

What is Duchenne muscular dystrophy?

A

The most common form of muscular dystrophy seen in children

39
Q

Describe the genetics of Duchenne muscular dystrophy

A

X-linked recessive disorders involving genes responsible for dystrophin, though one-third of cases are spontaneous mutations

40
Q

Describe the pathophysiology of Duchenne muscular dystrophy

A

Genetic mutation leads to an absence of dystrophin
Dystrophin is essential for cell membrane stability in muscle, causing progressive muscle degeneration

41
Q

What is Becker’s dystrophy?

A

A more slowly progressing form of muscular dystrophy in which there are some levels of dystrophin, but they are low

42
Q

How will Duchenne muscular dystrophy present?

A
  • Delay in motor development
  • Possible global delay
  • Pelvic and shoulder girdle weakness
  • Gower’s sign
  • Toe walking
  • Exaggerated lumbar lordosis
  • Calf hypertrophy
43
Q

What is the average age of onset in Duchenne muscular dystrophy?

A

3-4 years

44
Q

What is Gower’s sign in Duchenne muscular dystrophy?

A

Arms used to compensate for weakness of pelvic girdle muscles getting up from the floor

45
Q

What is the usual peak age of severe disability in Duchenne muscular dystrophy?

A

10

46
Q

What investigations are required in Duchenne muscular dystrophy?

A

CK
Molecular genetic testing
EMG
Muscle biopsy

47
Q

What are some management options used in Duchenne muscular dystrophy

A
  • No curative treatment
  • Gene-editing therapies in development
  • Steroids
  • Physiotherapy
48
Q

What is the typical age of death in DMD?

A

20-30 due to respiratory and cardiac involvement

49
Q

What is myotonic dystrophy?

A

The most common form of muscular dystrophy seen in adults

50
Q

Describe the genetics of myotonic dystrophy

A

Autosomal dominant mutation (2 different triple repeat mutations)

51
Q

When does the onset of myotonic dystrophy usually occur?

A

Between 20 and 50 years

52
Q

How does myotonic dystrophy present?

A
  • Myotonia
  • Weakness
  • Cataracts
  • Ptosis
  • Frontal balding
  • Cardiac defects
53
Q

What is myotonia?

A

Continued, involuntary muscle contraction after cessation of voluntary effort (failure of relaxation)

54
Q

What are some investigations required in myotonic dystrophy?

A

CK
EMG
Muscle biopsy
Genetic testing

55
Q

How is myotonic dystrophy managed?

A

Symptom management

56
Q

What is rhabdomyolysis?

A

A condition where skeletal muscle tissue breaks down and releases breakdown products into the blood, usually triggered by an event that causes the muscle to break down e.g. extreme underuse or overuse or a traumatic injury

57
Q

What are some causes of rhabdomyolysis?

A

Prolonged immobility
Extremely rigorous exercise beyond a persons fitness level
Crush injuries
Seizures

58
Q

What are some muscle products released into the blood in rhabdomyolysis?

A
  • Myoglobin(causingmyoglobinurea)
  • Potassium - the most immediately dangerous breakdown product as hyperkalaemia can cause arrhymias
  • Phosphate
  • Creatine kinase
59
Q

What are some clinical presentations of rhabdomyolysis?

A
  • Muscle aches and pain
  • Oedema
  • Fatigue
  • Confusion (particularly in elderly frail patients)
  • Red-brown urine
60
Q

What are some investigations required in rhabdomyolysis?

A
  • Raised creatine kinase
  • Urine - red-brown colour due to myoglobinurea, will be positive for blood
  • U&Es for AKI and hyperkalaemia
  • ECG is important in assessing the heart’s response to hyperkalaemia
61
Q

How is rhabdomyolysis managed?

A

IV fluids

62
Q

What are some complications of rhabdomyolysis?

A
  • Arrhythmias
  • Acute renal failure - breakdown products of the myocytes are toxic to the kidneys, particularly myoblobin
  • DIC
63
Q

What is the mechanism of necrotising myopathy?

A

Reduced essential co-enzyme production, myocyte membrane changes and increased oxidation

64
Q

What is the mechanism of corticosteroid myopathy?

A

Disruption of RNA synthesis

65
Q

What is the mechanism of mitochondrial myopathy?

A

Inhibition of mitochondrial DNA polymerase

66
Q

What is the mechanism of lysosomal storage myopathy?

A

Increase lysosomal activity causing muscle degradation

67
Q

What is the mechanism of antimicrotubular myopathy?

A

Accumulation of lysosomes and autophagic vacuoles

68
Q

What is the mechanism of hypokalaemic myopathy?

A

Disruption of water and electrolyte homeostasis

69
Q

What are some drugs causing necrotising myopathy?

A

Statins
Fibres
Nicotinic acid

70
Q

What are some drugs causing corticosteroid myopathy?

A

Fluorinated steroids (E.g. dexamethasone)

71
Q

What are some drugs causing mitochondrial myopathy?

A

Zidovudine (HIV drug)

72
Q

What are some drugs causing lysosomal storage myopathy?

A

Hydroxychloroquine
Amiodarone

73
Q

What are some drugs causing antimicrotubular myopathy?

A

Colchicine
Vincristine

74
Q

What are some drugs causing hypokalaemic myopathy

A

Diuretics
Oral contraceptive

75
Q

What are some drugs causing inflammatory myopathy?

A

D-penicillamine
Interferon-a

76
Q
A

Neurology (28 decks)

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