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YEAR 4 NEURO > Myasthenia Gravis > Flashcards

Myasthenia Gravis Flashcards

1
Q

Myasthenia Gravis is an __1___ disease which affects the ___2____. It is characterised by ___3____

A

Myasthenia Gravis is an ____autoimmune___ disease which affects the ___Neuromuscular junction ____. It is characterised by ___fatiguability____

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2
Q

Which skeletal muscle groups are affected in Myasthenia Gravis?

A
  • Extraocular muscles : common
  • Bulbar involvement: dysphagia, dysphonia, dysarthria

-Limb weakness – proximal symmetric

-Respiratory muscle involvement

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3
Q

Who gets Myasthenia Gravis? What kind of distribution is it?

A

Bimodal distribution.

20-30 yr females

60-80 yr males

More common in women (2:1) than men

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4
Q

What is the pathophysiology of Myasthenia Gravis?

A

Antibody mediated mechanism blocking Ach NMJ

IgG blocks Ach binding site on the synaptic membrane.

Ach rarely binds to the Ach receptor and Ach esterase begins to break it down

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5
Q

Myasthenia Gravis is linked to abnormalities in which lymphoid organ?

A

The thymus

abnormalities in 80% (LEC BB)

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6
Q

Which abnormalities of the thymus are linked to Myasthenia Gravis?

A

Thymic hyperplasia + Thymic tumours (thymoma)

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7
Q

What are some other asociated autoimmiune disorders with Myasthenia Gravis?

A

pernicious anaemia, autoimmune thyroid disorders, rheumatoid, SLE

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8
Q

Explain the link between thymic hyperplasia and Myasthenia Gravis
(LEC BB)

A

65% have early onset MG

-less common in ocular presentation

CT cannot identify hyperplasia

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9
Q

Explain the link between Thymic tumours and Myasthenia Gravis
(LEC BB)

A

30% get late onset MG

-Less common in ocular presentations

-Worse prognosis

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10
Q

What are the clinical manifestations of Myasthenia Gravis?

A

Fatiguability of skeletal muscle **

Ptosis

Extra-ocular muscle - complex opthalmoplegia

facial weakness

Muscles of limb and trunk can be affected

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11
Q

Myasthenia Gravis has a variable course, what can trigger episodes?

A

Stress
pregnancy / period
secondary illness
thyroid dysfunction
Trauma
temperature extremes
hypokalaemia
drugs ***
surgery

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12
Q

Name some commonly used drugs that affect the neuromuscular junction ?

A

AB - gentamicin, macrolides, quinolones (ciprofloxacin), tetracyclines

BP - B’blockers, CCBs, ACEi

Anaesthetics: Succinylocholine

Magnesium e.g. enema

Epilepsy: Phenytoin

Psych: Lithium

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13
Q

How does a myasthenic crisis present?

A

Slack facial muscles
drooling
Nasal speech
unsafe swallow
weak neck / jaw/ tongue / generally weak

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14
Q

How many pts get myasthenic crisis? what treatment will they need?

A
  • 15% to 20% of patients with MG experience a myasthenic crisis (an exacerbation necessitating mechanical ventilation)

acute treatment:
* Mechanical ventialtion
* IV intravenous immunoglobulin or plasma exchange.
* steroids
* supportive care: DVT prevention, sore prevetions, nutrition and fluid support

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15
Q

How does a cholinergic crisis present in Myasthenia Gravis?

A

overstimulation of nicotinic and muscarinic receptors at the neuromuscular junctions. This is usually secondary to the inactivation or inhibition of acetylcholinesterase (AChE). leads to excessive muscle simulation causing&raquo_space; flaccid paralysis

  • Resp failure (risk of sudden apnoea)
  • Miosis
  • SSLUDGE syndrome (salivation, sweating, lacrimation, urinary incontinence, diarrhoea, GI upset, hyper-motility, emesis)
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16
Q

What do you NOT find in Clinical manifestations of Myasthenia Gravis? (Differenciating from other conditions)

comment on:
Pupils
sensory
reflexes
autonomic

A

Pupils unaffected
No sensory loss
No reflex loss
No autonomic involvement

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17
Q

What investigations could you do for Myasthenia Gravis?

bedside
lab
special / imaging

A

Bedside:
* serial pulmonary function tests (SOB/ suspected Myasthenic crisis) - do FVC / NIF (negative inspiratory force) - both low in Mcrisis
* Ice test (ptosis gets better) (not as good as others below)

Lab:
* Serum Acetylcholine Receptir (AChR) antibodies - (+VE)
* muscle-specific tyrosine kinase (MuSK) antibodies (may be +ve if above not / unclear)

Imaging / special tests:
* repetitive nerve stimulation (>10% decline in compound muscle action potential (CMAP)

  • Single fibre electromyography EMG ( (increased variability (jitter) or / failure of neuromuscular transmission (block) in some muscle fibres)
  • CT thorax (thyomas or thymic enlargement)

BMJ BP

18
Q

What findings in electromyography for MG?

A

2 classic findings
*decrement in amplitude (progressive ‘fatigue’) of compound muscle action potentioal following repetitie muscle stimuation
* increased jitter using a single electrode

19
Q

Why is thymus imaging (CT/MRI) important in MG?

A
  • look for hyperplasia or tumour
  • removal of hyperplastic thymus improves the condition in some pts
  • removal of thyomas can stop malignant transformation
20
Q

What spirometery needs to be done with a pt with MG and why?

A
  • vital capacity (standing and lying) needs to be checked
    WHY
  • vital capacity falling below 1.5 L requires transfer to high dependancy / intensive unit BEFOFRE ventilatory failure occurs
21
Q

What antibodies can you test for in Myasthenia Gravis?

A

85-90% - AChR antibodies

40% have anti -muscle specific tyrosine kinase antibodies

  • often no AB seronegative in disease limited to ocular muscles
22
Q

What is the Tensilon Test?

A

To evaluate for Myasthenia Gravis

IV Edrophonium injected which temporarily reduces muscle weakness

23
Q

Contraindications for Tension test in Myasthenia Gravis?

A

Asthma
MI
bradycardia
risk of cardiac arrhythmia

24
Q

What are some important complications of myasthenia Gravis?

A

Respiratory :

Resp failure
Aspiration
Respiratory infection

25
Q

What is early / beside investigation for Myasthenia Gravis?

A

Bedside spirometry - looking at FVC

26
Q

What FVC readings need intervention in Myasthenia Gravis?

A

If falling or FVC <20ml/kg - senior review incase need ventilation

NOTE: Indications for mechanical ventilation are forced vital capacity (FVC) 15 mL/kg or less (normal ≥60 mL/kg) and/or negative inspiratory force (NIF) 20 cm H₂O or less (normal ≥70 cm H₂O)

27
Q

What blood gas results may you get in Myasthenia Gravis, what does this indicate?

A

HIGH CO2
LOW 02
acidosis

Type 2 respiratory failure

28
Q

How is Myasthenia Gravis managed / treated ?

A
  • Acetylcholinesterase inhibitors:
    Pyridostigmine (1st)

Immunosuppression:
- Corticosteroids: Prednisolone (start low)
- Steroid sparing : Azathioprine, cyclosporine

  • Thyectomy
  • regular neurology OP appts
  • mdt managament - OT, PT, SALT
  • plasmapheresis of immunoglobulins
29
Q

What is time of onset and duration of action for pyridostigmine?

A

Time onset of action - 60 mins

duration of action - 3-5 hours

patients response determines the dose

30
Q

what can overdoseage of pyridostigmine cause?

A

(often at start of usage) can cause a cholinergic crisis with severe weakess (can be hard to differenicate from myasthenic weakness)

31
Q

What are treatment options for managing an acute Myasthenic crisis?

A

Plasmapheresis
- removes AChR AB - short term improvement

Intravenous immunoglobulins
-60% respond within 7-10 days

32
Q

What safety netting information does the patient need to be told about myasthenia gravis?

A

Risk of certain drugs worsening condition e.g. antibiotics, cardiac, neuro, psychiatry

Risk of condition worsening after general anaesthesia

Advisable to carry a med-alert bracelet as conditions / inform health care workers e.g. pneumonia can make worse + AB e.g. doxycycline

33
Q

A pt with suspected Myasthenia gravis has an Xray. What abnormal finding might it show?

A

Smooth mass overlying aortic knuckle in anterior mediastinum = Thymic mass or Thyoma ( thymic disease associated with MG)

34
Q

What are the causes of an anterior mediastinal mass (four Ts)

A

Thymic mass/ thyoma

Thyroid mass

Teratoma

Lymp nodes (‘Terrible’lymphoma or carcinoma)

35
Q

What are some precipitants for a Myasthenic crisis?

A

Lots e.g.

emotion - stress
exercise
Pain
Sleep deprivation
Temp extremes
hypokalaemia
drugs e.g. b blockers, some AB

36
Q

What is the risk of Acetylcholinesterase inhibitor “over treatment” in a pt with Myasthenia Gravis?

A

Can cause a cholingergic crisis

37
Q

What spirometery needs to be done with a pt with MG and why?

A
  • vital capacity (standing and lying) needs to be checked
    WHY
  • vital capacity falling below 1.5 L requires transfer to high dependancy / intensive unit BEFOFRE ventilatory failure occurs
38
Q

Explain how myasthenic crisis leads to resp failure? what wil pt need?

A

Myasthenic crisis is characterised by worsening of muscle weakness, resulting in respiratory failure requiring mechanical ventilation.

39
Q

Respiratory failure in MG - what is measured in order to decide if mechanical ventilation is needed?

A
  • Serial measurements of forced vital capacity (FVC) are taken.
  • Indication for mechanical ventilation includes FVC 15 mL/kg or less (normal ≥60 mL/kg)
  • DO not wait for ABG as it occurs late in the course after clinical decompensation.
40
Q

List complicatoins of MG

A
  • Muscarinic adverse effects from medications - SLUDGE (loperamide for persisent diarrhoea/glycopyronium)
  • Respiratory failure (myasthenic crisis)
  • impaired swallow
  • acute aspiration
  • secondary pnyemonia
  • cardiac e.g. myocarditis
  • thyroid disorders
41
Q

What drugs can exacerbate Myasthenia Gravis:

A
  • Beta blockers
  • Lithium
  • Penicillamine
  • Gentamicin
  • Quinolones
  • Phenytoin

YEAR 4 NEURO (37 decks)

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