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gwen - neurology > Myasthenia Gravis and Lambert Eaton myasthenic syndrome > Flashcards

Myasthenia Gravis and Lambert Eaton myasthenic syndrome Flashcards

1
Q

What is myasthenia gravis?

A

This is an acquired condition characterised by autoimmune destruction of nicotinic acetylcholine receptors on the post-synaptic side of the NMJ. B and T cell mediated IgG autoantibodies are created which attack the postsynaptic acetylcholine receptors at the neuromuscular junction. This causes the physical symptoms of weakness and fatigability.

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2
Q

Aetiology myasthenia gravis

A

Autoimmune

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3
Q

What is the pathophysiology of myasthenia gravis?

A

Antibodies to acetylcholine receptor protein (anti-AChR antibodies) are commonly found. Immune complexes of anti-AChR IgG and complement are deposited at the postsynaptic membranes, causing interference with and later destruction of AChRs.

A second group of antibodies against muscle-specific receptor tyrosine kinase (anti-MuSK antibodies) have been identified in anti-AChR antibody negative cases. Ocular muscle MG is another subgroup.

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4
Q

What proportion of those with myasthenia gravis have thymic hyperplasia?

A

70% - below the age of 40

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5
Q

What proportion of those with myasthenia gravis have a thymic tumour?

A

10% - incidence increases with age

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6
Q

What disease processes are associated with the development of myasthenia gravis?

A
  • Thyroid disease
  • Rheumatoid disease
  • Pernicious anaemia
  • SLE
  • Thymic hyperplasia/thymoma
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7
Q

What age is myasthenia gravis more common in women?

A

<50 years

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8
Q

What age range is myasthenia gravis more commonly associated with being male?

A

>50 years

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9
Q

What are symptoms of myasthenia gravis?

A

Slowly increasing/relapsing muscular fatigue. Muscle groups affected include:

  • Extraocular
  • Bulbar
  • Face
  • Neck
  • Limb girdle
  • Trunk
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10
Q

What signs might you see in someone with myasthenia gravis?

A

Fatiguability demonstrated

  • Ocular - Ptosis (on sustained upward gaze), Diplopia, opthalmoplegia
  • Bulbar - dysphagia, dysphonia, dysarthria, dropping face
  • Peek sign
  • Voice fading - counting to 50
  • Downward drift when arms outstretched
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11
Q

What might patients with myasthenia gravis report with regards to their experience of their symptoms?

A

Best time is in the morning, and get worse as the day goes on (fatiguability)

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12
Q

What can exacerbate symptoms experienced in myasthenia gravis?

A
  • Pregnancy
  • Hypokalaemia
  • Infection
  • Over-treatment
  • Change of climate
  • Emotion
  • Drugs
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13
Q

What drugs can exacerbate myasthnic symptoms?

A
  • Gentamicin
  • Opiates
  • Tetracycline
  • Quinine
  • B-blockers
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14
Q

If someone presented with features of myasthenia gravis, what would be your differential diagnosis?

A
  • Polymyositis/other myopathies
  • SLE
  • Takayasu’s Arteritis
  • Botulism
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15
Q

What is the general couse of myasthnia gravis?

A

Has a fluctuating/relapsing/remitting course, but over time this progresses to severe disease, where respiratory difficulties become prominent

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16
Q

What effect does myasthenia gravis have on reflexes?

A

Normally preserved, but can demonstrate fatiguability

17
Q

What investigations might you do in someone with suspected myasthenia gravis?

A
  • Serum antibody - Anti-AChR antibodies, MUSK antibodies
  • EMG
  • Imaging - CT
  • Ice applicaiton test
  • Tensilon test
18
Q

What percentage of cases are anti-AChR antiobodies found in myaesthenia gravis?

A

80-90%

19
Q

What are the characteristic features of those with myaesthenia gravis with Anti-MUSK antibodies?

A

Weakness predominantly in bulbar, facial and neck muscles

20
Q

What might EMG show in someone with myaesthenia gravis?

A

A characteristic decrement with repetetive stimulation

21
Q

Why would you do a CT in someone with suspected myaethenia gravis?

A

To exclude Thymoma

22
Q

What is the tensilon test?

A

Not commonly used test

IV edrophonium - weakness improves within seconds, and can last up to 5 minutes

23
Q

How would you manage someone with myaethenia gravis?

A
  • Anticholinesterase - pyridostigmine
  • Immunosuppression - Treat relapse with prednisolone for extended period (depending on response)
    • ​Prednisolone (give osteoporosis prophylaxis)
    • Azathioprine or methotrexate
  • Thymectomy - beneficial even in those without thymoma
    • ​Consider if >50 and disease isnt controlled by anticholinesterases
    • IV Ig needed 5 days pre-op
  • Consider plasmapheresis/IVIG - exacerbation
24
Q

What are side effects to anticholinesterase medication?

A
  • Increased salivation, lacrimtion
  • Sweats
  • Comiting
  • Miosis
  • Diarrhoea
  • Colic
25
Q

What would you give in combination with steroid therapy for relapses of myaesthenia gravis?

A

Osteoporotic prophylactic treatment

26
Q

What is a myaesthenic crisis?

A

Life-threatening weakness of the resp. muscles during a relapse

27
Q

What else could be a cause of features of a myaesthenic crisis?

A

Cholinergic crisis - overtreatment with anticholinesterase drugs

28
Q

How would you manage someone with a myaesthnic crisis?

A
  • Monitor forced vital capacity
  • Ventilatory support
  • Identify cause (infection/meds)
  • Treat with plasmapheresis/IVIG
29
Q

DDx myasthenia

A

Botulism - rapid onset muscle weakness

MDN - generalsied weakness

30
Q

What is Lambert-Eaton myasthenic-syndrome?

A

Often a paraneoplastic manifestation of SCLC due to defective acetylcholine release at the NMJ. Can be caused by other disease processes including thyroid disease and T1DM

31
Q

What are antibodies in Lambert-Eaton-myasthenic syndrome against?

A

Voltage-gated Ca2+ channels on the pre-synaptic membrane

32
Q

What are features Lambert-Eaton Myasthenic Syndrome?

A
  • Gait difficulty preceding eye/Bulbar signs
  • Autonomic involvement
  • Hyporeflexia
  • Proximal limb weakness
33
Q

What autonomic features can present in Lambert-Eaton myasthenic syndrome?

A
  • Dry mouth
  • Constipation
  • Impotence
34
Q

What are features of proximal muscle weakness seen in Lambert-Eaton Myasthenic syndrome, and why does this differ from myasthenia gravis?

A

Tends to improve after a few minutes of muscle contraction

35
Q

How would you investigate someone for suspected Lambert-Eaton myasthenic syndrome?

A
  • EMG + repetetive stimulation
  • Serum antibodies - P/Q-type VGCC antibodies
36
Q

What proportion of those with Lambert-Eaton myasthenic syndrome are anti-P/Q type VGCC antibody positive?

A

85-95%

37
Q

How would you manage someone with Lambert-Eaton myasthenic syndrome?

A
  • Pyridostigmine
  • 3,4-Diaminopyridine
  • IVIG
38
Q

What would you consider doing in someone with diagnosed Lambert-Eaton myasthenic syndrome who had not been found to have SCLC?

A

Do regular high res CXR/CT - syndrome can precede cancer by > 4yrs

39
Q

How do anticholinesterase medications work?

A

Reduce the rate of degradation of ACh, thus increasing its chance of triggering an end-plate potential

gwen - neurology (38 decks)

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