myasthenia gravis Flashcards
mg definition
a chronic auto-immunye neuromuscular disease causing weakness in the voluntary (skeletal) muscles
mg caused by a reduced availability of ? at the NMJ
acetylcholine
which dysarthria would you expect with mg
flaccid only (failed muscle contractions, never spastic)
mg hallmark feature
- skeletal (voluntary) muscle weakness following periods of activity
- weakness rapidly improves after a period of rest
chronic or gradual onset in mg?
both
how does the neuromuscular junction work
- axons release neurotransmitter (acetylcholine)
- neurotransmitter travels across the synapse and attaches to receptors on the post-synaptic membrane
- receptors are stimulated which causes muscle contraction
mg pathophysiology
body makes antibodies to cockblock the acetylcholine from the receptors :(
- the immune system produces antibodies that interfere with the NMJ
- antibodies block, alter, or destroy receptors for acetylcholine at the NMJ
- prevents muscular contraction from occurring
2 prevalence peak decades in mg
- women: 20/30 years
- men: 70/80 years
gender ratio in mg
3:1, f:m
typical clinical features of mg
- fatigueable ptosis
- extraocular muscle weakness: diplopia, limitation of eye movements
- facial weakness
- weakness of eye closure
ptosis
eyelid drooping
what is the first symptom in 2/3 of mg patients
ptosis
diplopia
double vision
does mg have fasciculations?
no, only mnd
mg ocular muscle weakness features
fluctuating ptosis, diplopia
mg bulbar muscle weakness features
- dysarthria
- painless dysphagia
- dysphonia
- masticatory weakness
mg facial muscle weakness features
- facial weakness
- inability to close eye firmly
- drooling of saliva
mg axial muscle weakness features
flexion or extension of the neck
mg limb muscle weakness features
weakness involving the arms more than legs
mg respiratory muscle weakness features
- labor breathing
- orthopnea
- dyspnea
- respiratory failure
orthopnea
shortness of breath that occurs while lying flat and is relieved by sitting or standing
dyspnea
feeling short of breath
initial bulbar symptom in ?%
15%
bulbar signs in mg
- nasal regurgitation
- hypernasality
- difficulty masticating solids
- weak breathy voice quality
external contributing factors (that can trigger mg symptoms)
- emotional upset
- hypo-/hyperthyroidism
- menstrual cycle
- systemic illness
- pregnancy
- increased body temperature (hot baths, fireplace)
- meds affecting neuromuscular transmission
mg rating scale
- Osserman Classification System
Osserman Classification System
- Class 1 (any eye muscle weakness, possible ptosis, all other strength is normal)
to - Class 5 (intubation needed to maintain airway)
6 subtypes of mg
- ocular
- early onset
- late onset
- thymoma MG
- seronegative MG x 2
role of the thymus gland in risk factors for mg
- 10-20% of people with mg have a thymoma
- 20-40% of people with a thymoma will develop mg
full clinical evaluation
- elicit fatigue
- repeatedly blink (ptosis)
- upward gaze (double vision)
- count 1-100 (dysarthria)
- abduct arm (unilateral weakness)
- forced vital capacity
- hx thymoma
mg diagnostic tests
- tensilon (edrophonium) test
- ice-pack test
- electrophysiological tests (EMG, nerve conduction)
- auto-antibody test (blood test)
tensilon (edrophonium) test
- prolongs the duration of action of acetylcholine
- increases the amplitude and duration of the contractions
edrophonium chloride function
short-acting acetylcholinesterase inhibitor
tensilon (edrophonium) test sensitivity
71.5-95%
the tensilon (edrophonium) test is most reliable in people with ?
ptosis, nasal speech, or strabismus
important requirement before administering the tensilon (edrophonium) test
need to fatigue before administering it to see changes
MG prognosis
- relatively normal, not degenerative
- may go into remission temporarily and muscle weakness can disappear (discontinue meds)
MG management
- cholinesterase inhibitors
- corticosteroids
- plasma exchange
- immuno-suppression
- IVIG
- thymectomy
(MG management) cholinesterase inhibitors
- mimic neurotransmitters and prevent the breakdown of neurotransmitters
- manage fatigue
(MG management) corticosteroids
- complete relief of symptoms in most patients
- managing acute relapses
- reduce inflammation in the CNS
(MG management) plasma exchange
- 2nd line of therapy (after corticosteroids)
- blood filter to take out antibodies
- often 4-5 treatments over 2 weeks in hospital
(MG management) immuno-suppression
- stop the immune system from cockblocking the neurotransmitters
- prednisone
(MG management) IVIG
- intraveneous immunoglobulin
- injected with normal antibodies to change immune system responses
(MG management) thymectomy
remove enlarged or tumorous thymus
2 potential MG crises
- myasthenic crisis
- cholinergic crisis
myasthenic crisis
- severe weakness from MG
- need intubation for ventilatory support or airway protection
intubation for a myasthenic crisis is indicated if ?
- evidence of respiratory muscle fatigue
- increasing tachypnea
- declining tidal volumes, hypoxemia, hypercapnea, and difficulty handling secretions
favored treatment for myasthenic crisis
plasma exchange
cholinergic crisis
- overdose of cholinesterase inhibitors
- sweating, constricted pupils, excessive salivation, muscle fasciculations
thymectomy goal
stable, long-lasting remissions
MG SLT-related assessments
- MG-ADL
- MG-QOL15
SLT assessment in MG
- observe muscle fatigue at rest and during OMA
- check low tone/flaccidity in OMA
- evaluate over time
- stress/fatigue tests (count 1-100, include solids in swallow eval)
MG dysarthria
- hypernasality
- weak, breathy voice
- low volume
- misarticulation
- fatigability
dysarthria management
- observe the effects of medical intervention
- educate causes and factors affecting speech
- energy conservation (rest before conversation, short sentences, take breaks, calls early in day, non-verbal options, quiet environment)
NB for dysarthria management
- muscle strengthening exercises and speech drilling are contra-indicated
- can’t reverse neurotransmitter blocking
- will only worsen the dysarthria
possible prostheses
- ptosis props
- palatal lift prosthesis
prosis props
- hold eyelids up
- useful for reading books and watching movies
palatal lift prosthesis
- help hold up soft palate
- good for correcting hypernasality (not misarticulation)
- removed when eating and drinking
dysphagia in MG
- difficulty masticating solid foods (fatigue)
- nasal regurgitation of fluids
- weak tongue movements
- reduced hyolaryngeal excursion
- poor airway protection
- impaired UES tone
- weak cough
dysphagia management in MG
- observe effects of medicine
- education
- compensatory (small meals, small bolus, avoid chewy solids, multiple swallows)
NB for dysphagia management
direct rehab contra-indicated
