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Neurology > Disorders of the neuromuscular junction and muscle > Flashcards

Disorders of the neuromuscular junction and muscle Flashcards

1
Q

What are the disorders of muscle?

A

Myopathies
Myositis
Myotonic dystrophy

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2
Q

What may be seen in LMN disorders?

A

Weakness
Low tone
Fasciculations

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3
Q

Skeletal muscle fibres are innervated by _____ ______ whose cell _____ arise in the ______ horn of the spinal cord

A

Skeletal muscle fibres are innervated by motor neurons whose cell bodies arise in the ventral horn of the spinal cord

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4
Q

The terminal portion of these motor neurones give rise to very fine _________ that run along the muscle cell.

The synapses formed between motor neurons and muscle are called the _____ ___ plate

A

The terminal portion of these motor neurones give rise to very fine projections that run along the muscle cell.

The synapses formed between motor neurons and muscle are called the motor end plate

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5
Q

A single motor neurone may control ____ ______ cells but each muscle cell response to ____ ____ motor neuron

A

A single motor neurone may control many muscle cells but each muscle cell response to only one motor neuron

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6
Q

What is found on the end of the motor neurone?

A

ACh vesicles

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7
Q

What receptor are present on the muscle ?

A

ACh receptors

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8
Q

______ ______ moves along the nerve, _____ gated ______ channels open allowing influx of _____. Vesicles of _____ ______ are released into ______ ____.

A

action potential moves along the nerve, voltage gated calcium channels open allowing influx of calcium. Vesicles of acetyl choline are released into synaptic cleft.

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9
Q

____ _____ diffuses across the _____ ____. The _______ receptor opens and renders the membrane permeable to __/_ ions.
The ________ starts an ____ potential at the ____ ___ ___

A

Acetyl choline diffuses across the synaptic cleft. The acetylcholine receptor opens and renders the membrane permeable to Na/K ions.
The depolarisation starts an action potential at the motor end plate

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10
Q

__________ splits acetylcholine into _____ and ______ which is then sequestered into _______ _____

A

Acetylcholinesterase splits acetylcholine into acetate and choline which is then sequestered into presynaptic vesicles

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11
Q

What is curare?

A

d tubocurarine

A plant which occupies the same position on the ACh receptor but does not open ion channel

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12
Q

What does curare result in?

A

No muscle contraction- so no respiration

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13
Q

When is curare toxic?

A

IV or IM (1-15mins)

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14
Q

How does novichok work?

A

Inhibits cholinesterase

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15
Q

What conditions cause problems at the presynaptic motor neurone?

A

Abnormality of calcium, sodium or magnesium

Botulism

Lambert eaton myastheniac syndrome

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16
Q

Where is clostridium botulinum found?

A

In soil

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17
Q

What are the common mechanisms of becoming infected with botulinum clostridium?

A

Food and wounds can become infected.

IV drug users- black tar heroine

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18
Q

What does botulinum clostridium do?

A

Cleaves presynaptic proteins involved in vesicle formation and blocks vesicle docking with the presynaptic membrane

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19
Q

What are the symptoms of botulinum clostridium infection?

A

Rapid onset weakness without sensory loss/ Some medical and cosmetic uses)

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20
Q

What happens in LEMS?

A

Antibodies to presynaptic calcium channels leads to less vesicle release.

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21
Q

What is associated with Lambert eaton myasthenia syndrome?

A

Strong association with underlying small cell carcinoma.

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22
Q

What can Lambert eaton syndrome be treated with?

A

3-4 diaminopyridine

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23
Q

Myasthenia gravis is a ________ disorder, it is the _____ common disorder of the NMJ.

A

Myasthenia gravis is a postsynaptic disorder, it is the most common disorder of the NMJ.

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24
Q

What is the pathophysiology of MG?

A

Antibodies to acetylcholine receptors (AChR)

Recuded number of ACh receptors and flattening of endplate folds

Transmission becomes inefficient

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25
Q

What is the presentation of MG?

A

muscle weakness and fatiguability

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26
Q

When do symptoms of MG start?

A

When ACh receptors reduced to 30% of normal

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27
Q

ACh receptor antibodies are found in __-__% of patients

A

ACh receptor antibodies are found in 80-90% of patients

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28
Q

AChR antibodies block binding of Each but also trigger what?

A

Inflammatory cascade that damage the folds of postsynaptic membrane

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29
Q

The ______ plays a role in MG; __% of patients have _______ or _____

A

The thymus plays a role in MG; 75% of patients have hyperplasia or thymoma

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30
Q

When are the peaks of incidence of MG?

A

Females in 30s

Males in 60s or 70s

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31
Q

Female:Male ratio of MG

A

3:2

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32
Q

What are the clinical features of MG?

A

Weakness typically fluctuating- worse through the day

Most common presentation is with extra-ocular weakness, facial and bulbar weakness

Limb weakness is typically proximal

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33
Q

What is the acute medical treatment of MG?

A

Acetylcholinesterase inhibitor- pyridostigmine

IV immunoglobulin

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34
Q

What is the acute surgical treatment of MG?

A

Thymectomy- even in absence of thymus abnormality

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35
Q

What is the chronic medical treatment of MG?

A
  • Immunomodulating
  • Steroids
  • Steroid sparing agents- azathioprine/mycophenolate
  • Emergency treatment with plasma exchange or immunoglobulin
36
Q

What drug should be avoided in MG?

A

Gentamicin

37
Q

What do people with MG die of?

A

Respiratory failure and aspiration pneumonia

38
Q

Skeletal muscle is _____ organised.

A

Skeletal muscle is highly organised.

39
Q

What is the smallest contractile unit of skeletal muscle?

A

Muscle fibre- long, cylindrical, containing nuclei, mitochondria and sarcomeres

40
Q

What grounds the muscle fibre?

A

Endomysium

41
Q

__-__ muscle fibres are grouped to form ______ encapsulated by _______

A

20-80 muscle fibres are grouped to form fascicle encapsulated by perimysium

42
Q

A large number of fascicles ensheathed in epimysium forms

A

An individual muscle

43
Q

Describe smooth muscle

  • cell lay out
  • nucleus
  • junctions
  • surrounding tissue
  • cell structure
  • actin:myosin ratio
A 
Not striated
Single central nucleus
Gap junctions
Significant connective tissue
No sarcomeres
Actin myosin ration 10:1
44
Q

Describe type I muscle fibres?

A

Slow oxidative- dense capillary network, myoglobin, resist fatigue

45
Q

Describe type IIa muscle fibres?

A

Fast oxidative- aerobic metabolism

46
Q

Describe type IIb muscle fibres?

A

Fast glycolytic, easily fatigued

47
Q

What are fasciculations?

A

Visible, fast, fine, spontaneous twitch

48
Q

What can precipitate fasciculations?

A

Stress, caffeine, fatigue

49
Q

When do fasciculations occur pathologically?

A

In denervated muscle which becomes hyper excitable

50
Q

What are fasciculations usually a sign of?

A

Disease in the motor neurone not the muscle

51
Q

What is myotonia and what causes it?

A

Failure of muscle relaxation after use

Chloride channel

52
Q

What are the symptoms/signs of muscle disease?

A

Myalgia
Muscle weakness
Wasting
Hyporeflexia

53
Q

List the immune mediated muscle conditions?

A

Dermatomyositis

Polymyositis

54
Q

List the inherited muscle conditions?

A
  • Muscular dystrophies
  • Dystrophinopathies
  • Limb girdle muscular dystrophies
  • Myotonic dystrophy
55
Q

List the congenital muscle conditions?

A
  • congenital myasthenia syndromes

- congenital myopathies

56
Q

Describe the presentation of polymyositis?

A

Symmetrical, progressive proximal weakness developing over weeks to months
Raised CK

57
Q

What does polymyositis respond to?

A

Steroids

58
Q

Describe the presentation of dermatomyositis?

A

Clinically similar to polymyositis but associated with skin lesions- heliotrope rash on face

59
Q

What % of people with dermatomyositis have an underlying malignancy?

A

50%

60
Q

What is inclusion body myositis?

A

Degenerative disease, typically slowly progressive weakness in 6th decade of life with characteristic thumb sparing

61
Q

What is the prevalence myotonic dystrophy?

A

Commonest muscular dystrophy

62
Q

What is the genetic inheritance of myotonic dystrophy?

A

Autosomal dominant

Trinucleotide repeat disorder

63
Q

What is the presentation of myotonic dystrophy?

A

Multisystem involvement

Myotonia, weakness, cataracts, ptosis, frontal balding, cardiac defects

64
Q

What are muscular dystrophies?

A

Inherited noninflammatory progressive diseases. They have no central or peripheral nerve abnormality. DMD and BMD are the most common

65
Q

What are the infectious causes of muscle disease?

A

Viral- coxsacchie
Trypanosomiasis
Cistercercosis- uncooked pork
Borrelia

66
Q

What are the toxic causes of muscle disease?

A

Drugs

Venoms

67
Q

What are the congenital causes of muscle disease?

A

Congenital myasthenia syndrome, congenital myopathies

68
Q

Which drugs cause necrotising myopathies?

A

HMG-CoA reductase inhibitors (stains), fibres, nicotinic acid

69
Q

What are necrotising myopathies?

A

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

70
Q

What are corticosteroid myopathies?

A

Disruption of RNA synthesis

71
Q

Which drugs cause corticosteroid myopathies?

A

Fluorinated steroids such as dexamethasone and triamcinolone

72
Q

What are mitochondrial myopathies?

A

Inhibition of mitochondrial DNA polymerase

73
Q

Which drugs cause mitochondrial myopathies?

A

Zidovudine

74
Q

What are lysosomal storage myopathies?

A

Increased lysosomal activity degrading muscle fibres

75
Q

Which drugs cause lysosomal storage myopathies?

A

Hydroxychloroquine, amiodarone

76
Q

Which drugs cause antimicrotubular myopathies?

A

Colchicine, vincristine

77
Q

What are antimicrotubular myopathies?

A

Accumulation of lysosomes and autophagic vacuoles

78
Q

Which drugs cause hypokalaemic myopathies?

A

Diuretics, oral contraceptives

79
Q

What are hypokalaemic myopathies?

A

Disruption of water and electrolyte homeostasis

80
Q

What are inflammatory myopathies?

A

Activation of immune system, resembles autoimmune disease

81
Q

Which drugs cause inflammatory myopathies?

A

D-penicillamine and interferon-a

82
Q

What is Rhabdomyolysis?

A

Dissolution of muscle

Damage of skeletal muscle causes leakage of large quantities of toxic intracellular contents into plasma

83
Q

What are the causes of rhabdomyolysis?

A

Crush injuries, toxins, post convulsion, extreme exercise

84
Q

What is the triad of rhabdomyolysis?

A

Triad of myalgia, muscle weakness and myoglobinuria

85
Q

What are the complications of rhabdomyolysis?

A

Acute renal failure and DIC

86
Q

What should be looked for when examining muscle?

A 
Inspection- thin, wasted, fasciculation
Palpation
Strength resting- power across joints
Neck strength
Core strength
Fatiguability
87
Q

What is the MRC muscle power grading?

A

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

Neurology (41 decks)

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