Myasthenia Gravis Flashcards
which type of autoimmune disorder
II - antibodies against AChR form immune complexes and are deposited at post synaptic memrbane
most common age and sex
2 incidence peaks in childbearing females and older males
twice as common in women
who does MuSK predominantly effect
women
which muscles does it effect, and which group lof muscles can the disease solely present in
proximal limb muscles, bulbar and ocular - can have purely ocular disease
what is the main underlying pathology
antibodies present in the NMJ:
- attack the nicotnic ACh receptor - inconsistent generation of muscle fibre AP - skeletal muscle weakness
- produce inflammatory cascade - damage and destroy post synpatic membrane
what is seronegative MG
those who don have AChR antibodies, often have muscle specific tyrosine kinase antibodies
does seronegative MG present differently
Likely to have more mild disease, with weakness in ocular, bulbar, facial and neck muscles.
what is the role of muscle specific tyrosine kinase, which Ab are directed against in MuSK
helps to anchor AChReceptors at post synaptic folds
which paraneoplastic sydnrome is MG associated wtih
thymoma
which thymus problem is MG usually associated with
thymic follicular hyperplasia (70%)
what is the link between thymus and MG
unsure, associated with thymic follicular hyperplasia and thymoma in 70% and 10% cases
more so in young people
thymectomy is seen to be of benefit even in the absence of thymus abnormality
what are the classical features of the muscle weakness
- worsens on repetitive movement
- worsens throughout day
- eg may be fine in morning
is muscle pain present
no
which muscles are particularly affected?
extraocular muscles
- ptosis
- diploplia
are pupillary defects seen
no, only extraocular muscles
what test can be done that will improve ptosis in most patients
ice test - cool ≥2 mins with ice pack
if you pull on the patients upper lid what might happen to the contralateral lid
induce ptosis
what are symptoms of muscles in the throat and neck beingaffected
- dysphagia
- dysarthria
- facial paresis
how does involvement of the chewing and swallowing muscles present problems
patient may not be able to finish meal
choking
which limb muscles are often involved
proximal limb weakness
how does proximal limb weakness tend to present
difficulty getting out of chair or climbing stairs
is there muscle wasting?
no
is proximal limb weakness a early or late onset feature
late
weakness of which muscle in particular is a distinctive clinical sign as there are not many other diseases that cause this (not eyes)
neck flexion weakness, eg head feels heavy
respiratory muscle involvement
can cause SOB
MG crisis
caused by respiratory muscle weakness - if the SOB is bad enough that the patient requires mechanical ventilation it is MG crisis
what tests should be performed to investigate respiratory muscle function if the patient presents with SOB, or there is a suspected MG crisis
pulmonary function tests - FVC
investigations indicated for MG
serum analysis of antibodies
- 80-90% of patients have AChR antibodies, 70% of AChR seronegative pt have MuSK antibodies
do patients presenting withb ocular MG have more or less likelihood of having AChR antibodies ?
less, around 50%
what complications can impaired swallowing lead to
aspiration and 2y pneumonia
first line treatment
pyridostigmine - a cholinesterase inhibitor
how is pyridostimine adminstered, and when
PO or IV
30min prior to eating, a sustained release form is available for night time dosing
2nd line treatment for those who fail on pyridostigmine
corticosteroids eg prednisolone
what is the first line treatment for patients wtih ocular MG
corticosteroids
when is imunosuppression considered
when pt are on high dose of steroids, particualrly if they have co morbidities that complicate this eg diabetes, hypertension, glaucoma, obesity
which surgical procedure is shown to be of benefit in all pt
thymectomy - even if there is no abnormality
why is thymectomy of benefit, and is it good for both types of antibody related disease?
- thymoma has possibility of malingancy
- more effective in positive AChR antibodies than anti MuSK antibodies
management of acute disease
plasma exchange or IV immunoglobulin
mortality?
low, tends to occur from resp failure or aspiration pneumonia
which organisms is typically found in aspiration pneumonia
Klebsiella - red jelly sputum
when in the disease course does MG crisis usually occur
within the first 2 years of diagnosis
name 4 drug/classes that must be avoided
aminoglycosides, steroids, ciprofloxacin, beta blockers
aminoglycosides and MG
ipair neuromuscular transmission and can cause clinically significant muscle weakness - resp depression - crisis
steroids and MG - dangers
pt will be stabilized on a maintenance dose of prednisolone (±steroid sparing agent) , sudden increase/decrease can directly inhibit NM function - worsen status - crisis
