L7 Myasthenia Gravis Flashcards
(66 cards)
1
Q
where is the term myasthenia gravis derived from
A
greek
- my → muscle
- asthenia → weakness
gravis → severe
2
Q
what is myasthenia gravis
A
a chronic autoimmune neuromusclular disease characterised by weakness in voluntary skeletal muscle, fluctuating symptoms and a marked fatiguability effect
3
Q
key characteristics of MG
A
- skeletal muscle weakness after periods of activity
- rapid improvement after rest
- skeletal muscle weakness isolated to specific muscle groups
- chronic and gradual onset
4
Q
how does the neuromuscular junction work
A
- axons release the neurotransmitter acetylcholine
- acetylcholine travels across the synapse and binds to receptors on post-synaptic membranes
- receptors are stimulated by acetylcholine causing muscular contraction
5
Q
pathophysiology of MG
A
- antibodies are produced by the immune system
- they block, alter or destroy acetylcholine receptors at the neuromuscular junction
- this prevents proper muscular contraction
6
Q
global prevalence
A
100-200 per million
(700,000+ cases worldwide
7
Q
incidence
A
10-20 per 100,000 (likely underdiagnosed)
8
Q
when does prevalence peak in women
A
2nd/3rd decade
9
Q
when does prevalence peak for men
A
7th/8th decade
10
Q
prevalence sex ratio
A
3:1 female to male
11
Q
occular muscle signs
A
- fatigable ptosis (drooping eyelids) - first symptom in 2/3 of MG patients
- extraoccular muscle weakness leading to diplopia (double vision) with limited eye movements
12
Q
facial muscle signs of MG
A
- facial weakness
- weak eye closure
13
Q
how many cases have bulbar signs
A
15%
14
Q
bulbar muscle signs of MG
A
- nasal regurgitation
- difficulty chewing
- breathy voice
15
Q
respiratory muscle involvement in MG
A
can cause acute respiratory symptoms which is a medical emergency
16
Q
limb muscle signs of MG
A
worse after exercise or at the end of hte day
weakness involves arms more than legs
17
Q
contributing factors in MG
A
- emotional upset
- systemic illness (eg. viral infections)
- thyroid disorders (hypo/hyperthyroidism)
- pregnancy
- menstrual cycle
- increased body temperature
- medications affecting neuromuscular transmission
18
Q
what classification system is used for MG
A
osserman classification system
19
Q
class 1 of osserman classification system
A
- Any eye muscle weakness
- Possible ptosis
- All other muscle strength is normal
20
Q
class 2 of osserman classification system
A
- Mild weakness of other muscles; may have eye muscle weakness of any severity
- 2a → Predominantly limb or axial muscles weakness or both
- 2b → Predominantly oropharyngeal or respiratory muscle weakness or both
21
Q
class 3 of osserman classification system
A
- Moderate weakness of other muscles; may have eye muscle weakness of any severity:
- 3a → Predominantly limb or axial muscles weakness or both
- 3b → Predominantly oropharyngeal or respiratory muscle weakness or both
22
Q
class 4 of osserman classification system
A
- Severe weakness of other muscles; may have eye muscle weakness of any severity:
- 4a → Predominantly limb or axial muscles weakness or both
- 4b → Predominantly oropharyngeal or respiratory muscle weakness or both
23
Q
class 5 of osserman classification system
A
intubation needed to maintain airway
24
Q
what is the link between MG and the thymus gland
A
there is a link between MG and thymomas (tumours of the thymus gland)
25
what percentage of people with MG have a thymoma
10-20%
26
what percentage of people with thymoma develop MG
20-40%
27
what does evalution for MG involve
- Aimed at eliciting fatigue:
- Repeated blinking for ptosis
- Counting to 100 to assess dysarthria
- Abducting arm for unilateral weakness
- Forced vital capacity test
- Upward gaze for double vision
- History of thymoma
28
what tests can be used to diagnose MG
- Bedside Tests: Tensilon (edrophonium) and ice-pack test
- Electrophysiological Tests
- Auto-Antibody Tests
29
how does the tensilon (enrophonium) test work
- a short-acting acetylcholinesterase iniibitor prolnong acetylcholine action in the NMJ
- this increases the amplitude and duration of end-plate potentials
- it slows down the overt sypmtoms which confirms MG
30
what is the sensitivity of the tensilon (endrophonium) test in diagnosing MG
71.5-95%
31
what MG symptoms is the tensilon (endrophonium) test most reliable for
otosis, nasal speech and strabismus (eye misalignment)
32
6 treatment types for MG
- cholinesterase inhibitors
- corticosteroids
- plasma exchange (plasmapheresis)
- immunossuppression
- IVIG
- thymectomy
33
two examples of cholinesterase inhibitors
- neostigmine
- mestinon
34
cholinesterase inhibitors
- Provide symptomatic relief
- Allow acetylcholine to accumulate at the NMJ
- Prolongs effects of acetylcholine
- Has adverse effects.
35
corticosteriods
- Much improvement occurs in the first 6-8 weeks
- Strength may increase to total remission in the months that follow.
- Best responses occur in patients with recent onset of symptoms.
- The major disadvantages are the side effects.
36
plasma exchange (plasmaperesis)
- In plasmapheresis, blood is routed through a machine that removes plasma containing harmful antibodies and replaces it with antibody-free plasma.
- Often 4-5 treatments over a two week period in hospital.
37
example of a corticosteroid
prednisone
38
immunosuppression
- eg. prednisone
- Alter the body’s immune system and reduce production of the antibodies which cause myasthenia gravis.
39
what does IVIG stand for
intravenous immunoglobulin therapy
40
IVIG
Person is injected with normal antibodies that change the way your immune system acts.
41
thymectomy
- Recommended for most patients
- Most favourable response is 2-5 years after the surgery.
42
two potential medical events in MG
- myasthenic crisis
- cholinergic crisis
43
what is myasthenic crisis
Severe weakness requiring intubation for ventilatory support or airway protection.
44
indicators for intubation during myasthenic crisis
- Respiratory muscle fatigue, with increasing tachypnea, declining tidal volumes.
- Hypoxaemia, hypercapnea
- Difficulty handling secretions
45
preferred treatment for myasthenic crisis
plasma exchange
46
what is cholinergic crisis
Respiratory crisis due to cholinesterase inhibitor overdose.
47
symptoms of cholinergic crisis
- sweating
- constricted pupils
- excessive salivation
- muscle fasciculations
48
prognosis of MG
- Some cases may enter remission temporarily.
- Muscle weakness may disappear completely so medications can be discontinued.
- Thymectomy aims for stable, long-lasting remission
- Severe weakness may lead to respiratory crises requiring emergency medical care.
49
two MG rating scales
- MG-ADL
MG- QOL15
49
50
what is the MG-ADL
rating scale for myasthenia gravis which assesses activities of daily livnig
51
what is the MG-QOL15
rating scale for myasthenia gravis measuring quality of life
52
what is SLT's role in myasthenia gravis
- sometimes aid in differential diagnosis
- main role is managing dysarthria and dysphagia
53
SLT assessment components
- Observe muscle fatigue at rest and during oro-facial examination
- Check for low tone/flaccidity
- Evaluate over time → massively important to identify possible MG.
54
stress/fatigue test for speech
count from 1-100 and compare speech quality at the start and the end
55
stress/fatigue test for swallow
include solids (eg. apple, sandwich) in evaulations to assess mastitory fatigue
56
what type of dysarthria is present in myasthenia gravis
flaccid
57
flaccid dysarthria characteristics in MG
- Hypernasality, weak breathy voice, low volume
- Misarticulation
- Fatigability → speech deterioration over time
58
dysarthria management in MG
- Monitor effects of medical interventions.
- Educate patients about speech factors and energy conservation strategies.
59
examples of conservation strategies for dysarthria in MG
- Rest before conversations, use short sentences, take breaks.
- Calls earlier in the day, non-verbal communication options, quiet environments.
60
are muscle strengthening exercises recommended for MG
no, these are contraindicated due to the fatigability in MG
61
two examples of prostheses which may be used in MG
- Ptosis props.
- Palatal lift prostheses.
62
symptoms of dysphagia in MG
- Difficulty masticating solids.
- Nasal regurgitation of fluids due to weak velopharyngeal seal
- Weak tongue movement (lingual muscles)
- Reduced hyolaryngeal excursion (suprahyoid muscles).
- Poor airway protection (vocal cord adduction).
- Impaired upper eosphageal sphincter tone.
- Weak cough response (expiratory muscles).
63
dysphagia management in MG
- Observe effects of medical management.
- Educate patients.
- Direct rehabilitation strategies are contra-indicated.
64
compensation strategies for dysphagia in MG
- Small frequent meals, avoid chewy solids, smaller bolus sizes.
- Multiple swallows.
65
SLT role in differential diagnosis
- Myasthenia gravis will not present with fasculations unlike MND.
- Additionally, Myasthenia gravis has the fatiguability and rapid rest and recovery as a key characteristic which MND does not.
