Myasthenia gravis Flashcards
what are bulbar symptoms
dysarthria, dysphagia, fatigable chewing
myasthenia gravis is caused by
auto antibodies that block acetylcholine receptors
Generalized myasthenia gravis presentation
affects ocular muscles with variable involvement of bulbar symptoms (dysarthria, dysphagia, fatigable chewing)
limb respiratory muscle weakness symptoms fluctuate throughout the day and worse later in day.
ocular myasthenia gravis presentation
eyelid and ocular muscle weakness
what makes myasthenia gravis symptoms worse?
exercise, stress, infection and improve with rest
how do you diagnose myasthenia gravis?
based on serology via the acetylcholine receptor (AchR) antibody which is present in 85% of MG pts.
Can also see muscle specific tyrosine kinase receptor antibody (MuSK) which are seen in 50% of AchR antibody negative pts
Can be done via EMG too.
how to treat myasthenia gravis
treat symptomatic pts with pyridostigmine and/or immune (steriods, IVIG) therapies
in acute exacerbations or myasthenia crisis: Treat with IVIG or plasma exchange. Don’t pick steroids.
what medical conditions is myasthenia gravis associated with?
thymic hyperplasia, thymoma, and autoimmune thyroid dx.
what medical/lab tests should be done after a confirmed myasthenia gravis?
Need to get a TSH to evaluate for thyroiditis and CT of chest to look for mediastinal mass (thymoma)
algorithm for myasthenia gravis evaluation
what causes myasthenia crisis?
infection, surgery,
pregnancy or childbirth,
tapering of immunosuppressive meds,
medications (aminoglycosides and beta blockers)
Clinical features of Myasthenia Gravis crisis (chart)
Lambert Eaton myasthenic syndrome (LEMS) is
paraneoplastic syndrome seen with pts who have small cell lung cancer
Lambert Eaton myasthenic syndrome is similar to
myasthenia gravis has _ocular symptom_s and muscle weakness DTR is decreased or absent but these improve with repetitive muscle activation.
how to diagnose Lambert Eaton syndrome?
serology against voltage gated calcium channel antibodies.
pt has fatigable diplopia and has nocturnal nasal quality of speech. what do they have?
What is most common symptom?
this patient has myasthenia gravis - with fluctuating and fatigable weakness. can present as ocular myasthenia (limited only to extraocular muscles and eyelids) or a generalized dx.
Most common symptom is ocular muscle weakness and can see ptosis be unilateral or bilateral or switch overtime.
Pt has fatigue, diplopia and dysphagia for past two months. Exercises and tires easily. Has double vision at the end of the day and after a URI two weeks ago is very weak and tired. Has trouble swallowing and coughs while drinking. This is his CT scan. what does he have?
he has a thymoma with concurrent myasthenia gravis. See anterior mediastinal mass on CT and also 15% of myasthenia gravis pts develop thymoma
50-70% of thymoma pts have MG symptoms.
Treatment of myasthenia gravis is
high dose steroids in acute crisis are second line and they are there to maintain symptom control but onset is delayed so steroids are not recommended in acute crisis.
For acute crisis need to give IVIG or plasma exchange.
what is a myasthenic crisis?
severe weakness from myasthenia gravis that requires intubation.
See generalized weakness, respiratory symptoms, severe oropharyngeal weakness that results in dysphagia and aspiration.
where to place pt in potential myasthenia gravis crisis?
what to monitor in pts and how often?
ICU and monitor their respiratory status
q2-4 hour vital capacity and maximal inspiratory force
what happens to pyridostigmine with pts who have myasthenia crisis?
stop this while pts is on mechanical ventilation to minimize secretions and decrease aspiration risk. Can be restarted after extubation.
Is rituximab helpful for myasthenia gravis?
helpful for refractory myasthenia gravis in pts who have MG muscle specific tyrosine kinase antibodies
but NOT indicated or used in management of myasthenia crisis.
Diagnosis of Myasthenia Gravis is by
If this is negative what is done next?
Do we still diagnose based off edrophonium test?
serological testing: 85% of generalized MG will have positive acetylcholine receptor autoantibodies
50% of ocular MG will have positive AChR antibodies
40% of pts who are seronegative for AchR antibodies are positive for muscle-specific tyrosine kinase autoantibodies
If serology is completely negative, EMG and nerve conduction study is done with repetitive stimulation to confirm diagnosis.
We no longer do edrophonium and ice pack test due to high false positive rates.
4T’s of anterior mediastinal masses
thymoma’s - most common
teratoma - and other germ cells
thyroid gland or goiter
terrible lymphoma - located in middle or posterior medastinum.
Thymoma management
surgery in clinical setting with thymom and thymic carcinomas
Thymectomy is suggested for people who are <60 yrs and have generalized myasthenia gravis.
Lambert Eaten myasthenic syndrome is
paraneoplastic syndrome with small cell lung cancer that presents with slowly progressive proximal muscle weakness and decreased DTR, dry mouth, and ED.
See vigorous muscle activation improves with recovery of DTR and muscle strength.
Rarely see ocular symptoms.
back pain, paresthesias and symmetrical weakness worse in lower extremities and hyporeflexia
Guillain Barre syndrome or acute inflammatory demyelinated polyneuropathy
see ascending progressive symmetric weakness or paralysis after a week of URI or GI (campylobacter)
- 1/3 won’t have prior symptoms. As weakness ascends see weakness with walking, 3/5 strength of lower extremities compared to 4/5 strength of upper extremities in this pt.
See bulbar symptoms (ophthalmoplegia, facial diplegia, dysarthria, dysphagia) and respiratory compromise.
Back pain is from dx targeting the primary proximal polyneuropathy and pts having mild sensory symptoms such as paresthesias and sensory ataxia.
they can develop dysautonomia = tachycardia, diaphoresis and sluggish pupils and absent reflexes.
if suspecting acute inflammatory demyelinated polyneuropathy then need to get
LP - in all suspected GBS pts to rule out infectious causes and document elevated CSF protein in normal CSF WBC. See albuminocytologic dissociation.
LP is not diagnostic for GBS because it can see abnormal symptoms a week after symptom onset.
Nerve conduction and study and EMG are needed to confirm GBS.
Pt has fatigue, diplopia and dysphagia for past two months. Exercises and tires easily. Has double vision at the end of the day and after a URI two weeks ago is very weak and tired. Has trouble swallowing and coughs while drinking. This is his CT scan. what does he have?
he has a thymoma with concurrent myasthenia gravis. See anterior mediastinal mass on CT and also 15% of myasthenia gravis pts develop thymoma
50-70% of thymoma pts have MG symptoms.
Treatment of myasthenia gravis is
high dose steroids in acute crisis are second line and they are there to maintain symptom control but onset is delayed so steroids are not recommended in acute crisis.
For acute crisis need to give IVIG or plasma exchange.
First line treatment for GBS and myasthenia crisis?
Give IVIG or plasmapheresis. Don’t pick steroids
Myasthenia gravis crisis - steroids helps to keep things calm over time not best in acute crisis.
GBS- steroids are not helpful.
