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Neurology Week 5 2018/19 > 6: Neuromuscular disorders > Flashcards

6: Neuromuscular disorders Flashcards

1
Q

What is the neuromuscular junction?

A

Synapse between LMNs and muscle fibres

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2
Q

Which horn of the spinal cord contains motor neurons?

A

Anterior (ventral horn)

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3
Q

What is a motor end plate?

A

The muscle-end of the neuromuscular junction

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4
Q

Each motor neuron may supply (one / many) muscle(s).

Each muscle is supplied by (only one / many) motor neuron(s).

A

many

only one

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5
Q

Which neurotransmitter passes into the synaptic cleft of the NMJ in response to an action potential?

A

ACh

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6
Q

Which ions are involved in the wave of depolarisations along a nerve axon?

A

Na+ IN

K+ OUT

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7
Q

Which ion triggers the release of neurotransmitter into the synaptic cleft of the NMJ?

A

Ca2+

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8
Q

Which enzyme clears up remaining ACh from the synaptic cleft?

A

Acetylcholinesterase

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9
Q

Which toxin occupies ACh receptors in the synaptic cleft, preventing muscle contraction?

A

Tubocurarine

‘flying death’, poison arrows etc.

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10
Q

Which receptor is blocked by tubocurarine?

What happens as a result?

A

ACh receptor

Muscle paralysis (inc. respiratory)

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11
Q

Which poison inhibits acetylcholinesterase, causing muscle paralysis and death?

A

Novichok

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12
Q

What cannot be released if there is a problem with the Ca2+ channels of the pre-synaptic neurons involved in NMJs?

A

ACh

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13
Q

What is botulism?

A

Infection by Clostridium botulinum

Which produces Botulinum toxin

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14
Q

What is the effect of botulinum toxin?

Why?

A

Muscle weakness

Blocks ACh release at pre-synaptic terminal

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15
Q

How do the following nerve agents affect the neuromuscular junction?

a) tubocurarine
b) NOVICHOK
c) Botulinum toxin?

A

a) ACh receptor antagonists

b) Acetylcholinesterase inhibitor

c) Blocks secretion of ACh at pre-synaptic terminal

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16
Q

Name an autoimmune disease which affects the neuromuscular junction at the

a) post-synaptic
b) pre-synaptic end?

A

a) Myaesthenia gravis

b) Lambert-Eaton syndrome

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17
Q

What is the main symptom of Lambert-Eaton syndrome?

A

Muscle weakness

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18
Q

What condition is Lambert-Eaton syndrome associated with?

A

Small cell lung cancer

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19
Q

What antibodies are produced in Lambert-Eaton syndrome?

A

Ca2+ channel antibodies

So not as much ACh is released into NMJ, causing muscle weakness

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20
Q

The drug 3-4-diaminopyridine is used to treat symptoms of Lambert-Eaton syndrome.

How does it work?

A

Blocks K+ channels

So action potential lasts for longer, more Ca2+ has the chance to enter the pre-synaptic terminal and more ACh can be secreted into the NMJ

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21
Q

What is a rare post-synaptic disorder causing muscle weakness and fatigue?

A

Myaesthenia gravis

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22
Q

Myaesthenia gravis is an ___ disease.

A

autoimmune

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23
Q

When does the incidence of myaesthenia gravis peak?

A

Early 20s

Elderly

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24
Q

What is the pathophysiology of myaesthenia gravis?

A

Autoimmune disease

Autoantibodies BIND TO ACh receptors of neuromuscular junction

Resulting in muscle weakness and fatigability

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25
Q

Which antibodies are seen in 90% of patients with myaesthenia gravis?

A

ACh receptor antibodies

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26
Q

Which immune organ undergoes hyperplasia in myaesthenia gravis?

A

Thymus

Particularly in young people

27
Q

(Men / women) tend to develop myaesthenia gravis.

A

Women

autoimmune disease

28
Q

What is the course of weakness seen in myaesthenia gravis?

A

Fluctuating

29
Q

Which muscles tend to be affected in myaesthenia gravis?

A

Extraocular muscles

Facial muscles

Bulbar muscles (chewing, speaking, swallowing)

30
Q

What tends to cause death in late myaesthenia gravis?

A

Respiratory muscle weakness

31
Q

Which movements can you ask a patient to do to investigate suspected myaesthenia gravis?

A

Blinking

Neck flexion

32
Q

What is the acute management of myaesthenia gravis?

A

Acetylcholinesterase inhibitor e.g pyridostigmine

IV Ig - for autoimmune problem

Thymectomy - surgical removal of thymus

33
Q

What does testing blinking and neck flexion in a myaesthenia gravis patient demonstrate?

A

Muscle fatigability

34
Q

What is the long-term pharmacological management for myaesthenia gravis?

A

Immunosuppression:

Steroids

Steroid-sparing DMARDs - azathioprine, mycophenolate mofetil

35
Q

Which antibiotic should you avoid in patients with myaesthenia gravis?

Why?

A

Gentamicin

Aminoglycoside antibiotics cause Myaesthenic crisis - respiratory failure, aspiration pneumonia

36
Q

What is a myaesthenic crisis?

A

Emergency presentation of myaesthenia gravis

Respiratory depression due to weakness of intercostal muscles, inability to breathe +/- aspiration pneumonia, brought on by drugs including gentamicin

37
Q

How is a myaesthenic crisis treated?

A

Intubation

High dose corticosteroids

Plasma exchange / immunoglobulin

38
Q

Describe how smooth muscle looks under the microscope.

A

Non-striated

Single, central nucleus

39
Q

Describe how cardiac muscle looks under the microscope.

A

Striated

Single, central nucleus

40
Q

Describe how skeletal muscle looks under the microscope.

A

Striated

Multiple nuclei found at the cell membrane

41
Q

What colour are muscle fibres which rely on

a) aerobic respiration
b) anaerobic respiration?

A

a) Red

b) White

42
Q

What are type I muscle fibres also known as?

What type of activity are they best for?

A

Slow oxidative

Long duration exercise e.g distance running as they fatigue slowest

43
Q

What are type IIa muscle fibres also known as?

What activities are they best suited for?

A

Fast oxidative

Medium intensity, longer duration exercise e.g a 1000m race, fatigue faster than type I fibres

44
Q

What are type IIb muscle fibres also known as?

What activities are they best suited for?

A

Fast glycolytic

Rely on glycolysis only, so fatigue quickly; best for sprinting, weightlifting over a very short duration

45
Q

What are the functional units of muscle called?

A

Sarcomeres

46
Q

What is a fasciculation?

A

Visible muscle twitch

47
Q

Abnormal fasciculations indicate a problem with the (motor neuron / muscle).

A

motor neuron

specifically the LMN

48
Q

What is myotonia?

A

Failure of muscle after being used (e.g patient can’t release from a handshake)

49
Q

What ion is involved in myotonia?

A

Cl-

50
Q

What are some inflammatory myopathies which cause muscle weakness?

A

Polymyositis

Dermatomyositis

Inclusion body myositis

51
Q

Which type of myositis is atypical, develops in your 60s and spares the thumb?

A

Inclusion body myositis

52
Q

What does dystrophy mean?

A

Abnormal atrophy of a structure (usually muscle)

53
Q

What is a genetic disease causing

myotonia

muscle weakness

cardiac problems

ptosis, frontal balding and cataracts?

A

Myotonic dystrophy

54
Q

What is the mode of inheritance of myotonic dystrophy?

A

Autosomal dominant

55
Q

Apart from myotonic dystrophy, what are two other common dystrophic diseases you need to know?

A

Muscular dystrophy

Duchenne and Becker

56
Q

Myotonic dystrophy is caused by abnormal trinucleotide repeats and shows anticipation, meaning that the further down a family tree you go, the more likely you are to inherit it.

Which other neurological disease behaves like this?

A

Huntington’s disease

CAG repeats with anticipation

57
Q

Is muscular dystrophy an inflammatory problem?

A

No

58
Q

Duchenne and Becker muscular dystrophies affect only ___.

A

boys

X-linked recessive inheritance

59
Q

What are the symptoms of muscular dystrophy?

A

Progressive muscle weakness and wasting

60
Q

What are important drugs which cause myopathy as a side effect?

A

Statins

Steroids (if used for long enough, also atrophy)

61
Q

What is rhabdomyolysis?

A

Skeletal muscle damage releases toxins into bloodstream

62
Q

What are some common causes of rhabdomyolysis?

A

Extreme exercise

Crush injury

Status epilepticus

63
Q

Which organs are damaged by rhabdomyolysis?

A

Kidneys

Neurology Week 5 2018/19 (11 decks)

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