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Neurology > Neuromuscular Disease > Flashcards

Neuromuscular Disease Flashcards

1
Q

Describe the functioning of the neuromuscular junction (NMJ).

A
  1. Action potential reaches presynaptic terminal of motor neuron.
  2. This opens presynaptic Ca channels which allow Ca to flow into the cell
  3. Ca triggers vesicular release of ACh into the synaptic cleft.
  4. ACh binds to an post synaptic ACh receptor on the muslce fibre.
  5. This causes muscle fibre depolarisation which contracts the muscle.
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2
Q

What condition of the neuromuscular junction affects presynaptic channels? Which channel does it affect?

A

Lambert Eaton Myasthenic Syndrome

Presynaptic Ca channels

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3
Q

What causes Lambert Eaton Myasthenic Syndrome?

A

Autoantibodies produced by body or small cell lung cancer attack presynaptic Ca channels, damaging the neuromuscular junction and preventing muscle contraction.

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4
Q

How does Lambert Eaton Myasthenic Syndrome present?

A

Intially lower limb weakness

With possible autonomic features (dry mouth, postural hypotension, dysphagia)

Later, may get eye symptoms (ptosis, diplopia)

In a patient with risk factors (smoking, family history, other autoimmunity)

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5
Q

How do you diagnose Lambert Eaton Myasthenic Syndrome?

A

Nerve conduction study

consider autoantibodies but often negative

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6
Q

How do you treat Lambert Eaton Myasthenic Syndrome?

A

Amifampridine

IV Ig if severe

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7
Q

What condition of the neuromuscular junction affects postsynaptic channels? Which channel does it affect?

A

Myasthenia Gravis

Post synaptic ACh receptors

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8
Q

What causes myasthenia gravis?

A

Autoantibodies (AChR, MuSK) attack postsynaptic ACh receptor, damaging the neuromuscular junction and preventing contraction.

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9
Q

How does myasthenia gravis present?

A

Starts with facial muscle weakness
(ptosis, diplopia)
(mastication weakness, dysphagia)

Fatigue improves with rest, worst at end of day

Generalised limb weakness later

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10
Q

How do you diagnose myasthenia gravis?

A

Autoantibody testing (AChR/MuSK)

EEG if clinical suspicion but negative for autoantibodies

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11
Q

How do you treat myasthenia gravis?

A

Pyridostigmine (+/- steroids)

Thymectomy

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12
Q

What is myasthenic crisis and how do you treat it?

A

Worsening of myasthenia gravis causing respiratory failure

IV immunoglobulin

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13
Q

What drug should be avoided in myasthenia gravis and why?

A

Gentamicin

Can cause myasthenic crisis

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14
Q

What are the main differences between Lambert Eaton Myasthenic Syndrome (LEMS) and Myasthenia Gravis (MG) in terms of

  1. pathophysiology?
  2. presentation?
  3. treatment?
A

1.
LEMS caused by autoimmune/paraneoplastic (SSLC) damage to presynaptic Ca channels.
MG caused by autoimmune damage to postsynaptic ACh channels

2.
LEMS starts with limb weakness (autonomic features) and progresses onto ocular symptoms.
MG starts with ocular symptoms (and fatigue) and progresses onto limb weakness

3.
LEMS - Amifampridine
MG - Pyridostigmine

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15
Q

What causes myotonic dystrophy?

A

Autosomal dominant tri-nucleotide repeat causing myotonia and muscle wasting

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16
Q

How does mytonic dystrophy present?

A 
In mid 20s
Distal limb myotonia and weak neck
Muscle wasting
Cataract
Frontal balding
17
Q

What is motor neuron disease and what characterises it?

A

Neurodegenerative condition

Upper AND lower motor neuron signs

18
Q

What gene is associated with motor neuron disease

A

C9orf72

19
Q

Risk factors for motor neuron disease.

A

Family history

Smoking

Professional athletes (and military service)

20
Q

What investigation is diagnostic of motor neuron disease?

A

None

MND is a clinical diagnosis.

21
Q

Name 4 upper and lower motor neurons signs that you may see in motor neuron disease.

A

Upper

  • stiffness
  • spasticity
  • hyper-reflexia
  • painful spasms

Lower

  • weakness (foot/head drop)
  • muscle atrophy (split hand sign)
  • increased lumbar lordosis (axial weakness)
  • dyspnoea (diaphragm weakness)
22
Q

Commonest form of motor neuron disease.

A

Amyotrophic lateral sclerosis

23
Q

What neurons are affected in amyotophic lateral sclerosis (ALS)?

A

Upper motor neurons (somatosensory cortex)

Lower motor neurons (ventral horn of spinal cord)

24
Q

Patient with motor neuron disease has cognitive decline.

  • what form of MND do they have?
  • what is causing cognitive decline?
  • what test might you consider?
A

Amyotrophic lateral sclerosis

Frontotemporal dementia

C9epo72 gene testing (associated with ALS-frontotempoeral dementia)

25
Q

Describe the presentation of amyotrophic lateral sclerosis.

A

Upper and motor neuron signs starting distally and progressing proximally

26
Q

Name the form of motor neuron disease which

  • affects upper and lower motor neurons
  • affects upper motor neurons
  • affects lower motor neurons
  • affects cranial nerves
A

Upper and lower: amyotrophic lateral sclerosis

Upper: primary lateral sclerosis

Lower: progressive muscular atrophy

Cranial nerves: progressive bulbar palsy

27
Q

How does primary lateral sclerosis present?

A

Spasticity, painful cramps, hyperreflexia

Without muscle atrophy

(only affects upper motor neurons)

28
Q

How does progressive muscular atrophy present?

A

Muscular atrophy, fasciculations, weakness

only affects lower motor neurons

29
Q

How does progressive bulbar palsy present?

A

Fasciculating tongue, speech/swallowing difficulty, emotional lability

30
Q

What cranial nerves are affected in progressive bulbar palsy?

What functions of these nerves are relevant to the presentation of progressive bulbar palsy?

A 
CN IX (glossopharyngeal)
- stylopharyngeus elevation (swallowing)

CN X (vagus)

  • pharyngeal muscles (swallow)
  • laryngeal muscles (speech)
CN XII (hypoglossal)
- tongue motor (swallow/speech)
31
Q

Patient with motor neuron disease has emotional lability.

  • what form of MND do they have?
  • what is causing emotional lability?
A

Progressive bulbar palsy

Pseudobulbar affect (emotional incontinence caused by brain damage)

32
Q

How do you manage a patient with motor neuron disease?

A

Supportive (communication/nutrition/respiratory aids)

33
Q

What drug can be used for motor neuron disease?

What is its mechanism of action?

Why might it not be used?

A

Riluzole

Na+ channel blocker, prevents glutamate release and neurotoxicity

Expensive, lots of side effects and only gives 3 months extra life

Neurology (11 decks)

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