Myasthenia Gravis Flashcards
what is myasthenia gravis
acquired auto immune disorder affecting nmj
excessive fatigue of striated muscle
longer term permenant deterieration and muscle weakness
affects nmj- multiple sclerosis = similar
longer you have myasthenia - higher risk of permeant derivation
signs and symptoms are variable and are dependent on when you are seen
what are some of the symptoms of mystenia gravis
breathing difficulty
difficulty to chew or swallow
difficulty to climb stairs , lift objects
difficulty in talking
drooping position of head
change in voice
facial paralysis
fatigue
weakness of eye muscles
what is the incidence of myasthenia gravis
incidence= 5/7 rare
affects women more than it affects men but they are increasingly affected over the age of 40
very variable
complete remission in 18% of patients
can be 40 yrs between firsts signs and next episodes
what is the aetiology of mg
antibodies to nicotinic ach receptors reduce post synaptic receptors by degrading receptor proteins
directly blocking receptor sites
destroying receptor sites
(more difficult for ach to reach the muscle and hit it)
what antibodies are found to other proteins in mg
muscle specific kinase
can lead to neurotransmission
problems at nmj
lrp4 - can be found in mg and ocular mg
how can the nmj be affected in mg
surface area = degraded in mysthemia
muscle contraction is less
how does the aetiology of mg cause muscle fatigue
ach continues to be released from the presynaptic membrane until supplies are diminished - resulting in muscle fatigue
common eye signs can be - proptosis and ptosis
what is commonly found in patients with mg
85% of mg patients have nicotinic ach receptor antibodies circulating in the blood
post synaptic membrane of nmj is less folded in mg patients and synaptic space is wider
enlarged thymus glands - antigen antibody reaction between endplate protein and thymus epitheliel cells
what is the function of the thymus gland
- in children and babies - has a major role in puberty
- programmes abc into attacking invading foreign cells such as viruses
important in normal immune response development
what is the role of the thymus gland in mg
it is enlarged in approx 75% of mg cases - thymomas in some patients - especially over the age of 40
thymus removal cures 35% and improves a further 33% of patients
thymectomy even effective in cases of non thymomamtmus mg with remission rate higher than for non surgical treatment (catalo et al 2018)
removal advocated in mg patients between 10-40 years of age within the first 3 years of disease onset
what are the classifications of mg
paediatric- neonatal, congenital, juvenile
adult- ocular, mild/moderate, acute fulminating , late severe
how is the severity of mg classified
grade 1 = less severe - restricted to eom only
grade 4 = myasthenia crisis
what is drug related mg
following d peniclliamine for rheumatoid arthritis
some antibiotics cardiovascular agents , anti-depressants , sedatives , anaesthetics, can induce or aggravate the condition
important to note this in history
what muscle groups are affected on mg
eom - diplopia and ptosis are the presenting feature in 50% of cases and will be present in 90% of patients
bulbar muscles - innervated by cranial 5, 7, 9, 10,
limb/ trunk muscle - 15- 20% start with arm or leg weakness
weakness of intercostal muscles causing breathing problems
what is the natural history of mg
variable disease affecting individuals very differently sometimes mimics other diseases
if onset initially in eom prognosis better than if in limbs
disease may peak 2-5 years from onset that improve
periods of remission = quite common
mg = 50 times more common in graves disease patients
what is a myasthenia crisis
classed as a medical emergency
intercostal muscles are affected and mg patient is unable to breathe without ventilator
15- 20- % of generalised mg patients will have at least one myasthenia crisis
50% of known cause others triggered by stress, infection , surgery or drug sensitivity
what is ocular mg
may mimic any pupil sparing painless eye movement problem
unilateral or bilateral- 3rd, 4th, 6th nerve palsy
isolated muscle palsy - gaze palsy , one and a half syndrome
gaze palsy INO, one and a half syndrome ( 3rd year)
extremely variable = may change muscles from one visit to the next - hard to diagnose
what are common ocular presenting features on ocular mg
diplopia and ptosis are present in 75% of cases
10-16% of all mg is confined to the eyes
if no spread to other muscle groups within the first 2 years of onset it is unlikely to ever to do so
why are eom particulary affected
eom are highly innervated with densely concentrated receptors - small reduction in ach receptors and ach levels quickly result in fatigue
increased sensitivity of eom nmj
specific antibodies direct at specific sites on eom
what are some clinical features of ocular myasthenia
ptosis - unilateral or asymmetrical or bilateral
may increase on least affected side if examiner holds most affected lid
fine fluttering lid movements
patient may use brow to lift lid or adopt app (upper eyelid fold may be reduced/ absent)
what are some lid abnormaliies seen in mg
afternoon ectropion
- through reduced nmj activity and your muscles not working not working the bottom lid begins to droop
what are other lib abnormalities seen
cogans lid twitch - lid twitchs upwards
and overshoots before settling on moving from depression to normal
lids forced open easily - (weak obicularis)
lids separate slightly on voluntary closure
nystagmoid jerks of upper lid ( rare )
can mg be cured
cannot be completely cured can go into periods of remission, autoimmune disorder
what would be included in the orthoptic investigation
history- medication , fatigue , arm weakness
eyelid assessment - measure ptosis- if stable give fresel prism
why is the diagnosis of mg hard to arrive at
can be difficult as weakness is a common complaint of many diseases
correct diagnosis is important so that appropriate treatment can be offered
what tests are used in the diagnosis of mg
tension test - 10 mg injected intravenously (2mg initially followed by rest )
intravenous atropine if side effects occur
improvement in 1 min lasts ofr 5 mins
positive response - diagnostic but negative response cannot exclude diagnosis
because there are multiple receptors involved
blood test for ach receptor site antibodies
presence suggests mg = highly probable
absence cannot exclude disease
anti musk antibody test - present in 50% of those who don’t show ach receptor site antibodies
absence doesn’t exclude mg
what other tests can be used in the diagnosis of mg
sleep test - improvement after 30 mins in darkened room - ask pt to go to sleep for 30mins and try and see them upon waking
symptoms may reappear 1-5 mins after reawakening
repeptitive nerve stimulation
saccadic velocity measurement
EMG
single fibre emg
what other diagnostic tests may be done If mg = suspected
ct scans of chest to check for enlarged thymus/thyoma
chest xray
what are the general treatment options for mg
long acting ach drugs
immunosuppressive agents
plasmapheresis
intravenous immunoglobins
thymectomy (not for ocular mg) appears effective in the treatment for non - thymotoamous mg ) cataneo et al 2018)
ocular management
plotting course of disease / serial record
prisms or occlusion to make patient comfortable
ptosis props
botulinum toxin a injection
strabismus surgery if really stable
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