Myasthenia Gravis Flashcards
what is myasthenia gravis
LMN myopathic disorder w NM junction pathophysiology
what is the pathophysiology of MG
autoimmune dz
antibodies produced against ACh receptors of postsynaptic membrane at the NMJ
bind to ACh receptors and causes destruction
ACh unable to bind to post-synaptic membrane
dec amp in end-plate potentials
dec action potentials and weak ms contraction
is MG hereditary
not a genetic health condition
however, inc risk of MG if there is an autoimmune d/o (thyroid dz, RA, lupus) in the family
what are 3 possible etiologies of MG
inc risk if autoimmune in fam
viral/bacterial trigger
thymus gland link
how has MG been possibly linked to thymus gland as an etiology
thymus gland involved w immune cell production
- programs T cells to recognize self vs non-self
tumor of thymus gland or thymic hyperplasia seen in people w MG
- possible that T cell malfunction results in autoimmune attack
what is the general pattern seen in the demographics of prevalence of MG
more common in <50yo F
more common in >50yo M
why can it be difficult to initially dx MG
fluctuation in sx
- sx may also be mild at first
how is MG dx
presence of Ab in antibody testing + clinical presentation* confirms dx
*clinical s/sx
differentials r/o
- psych d/o
- stroke/TIA
- MS
- ALS
- other NM d/o
(don’t need antibody testing to be dx w MG - can be dx based of clinical sx w differentials r/o)
what is antibody testing for MG
antibodies (Ab) against ACh receptors present in 90% of pts w MG (seropositive)
seronegative doesn’t fully r/o MG
what are all the dx tests for MG
antibody testing
blood serum testing
EMG studies
Tensilon test
MRI/CT of thymus
what would EMG studies show in MG
rapidly declining action potential in ms upon repeated nerve stim
what does tensilon (edrophonium) test for in MG
rapid acting cholinesterase inhibitor admin via IV
- produces temp inc in strength of contraction
how are clinical subgroups of MG organized
age of onset
- neonate, juvenile, early, late
seroneg MG (no Ab)
location of weakness
- thymus tumor, eye, generalized
what are clinical features of MG
facial, eye neck weakness
- asymmetrical, fluctuating
ptosis
weakness of oropharyn ms
- dysphag, dysart, nas speech
impacts respiratory ms
fatigue/weakness w activity
what is the most common motor sx
ptosis
how does fatigue and weakness often present in MG and how is this an education point for us
worse w activity
relieved by rest
provide ed on pacing
more strenuous activities early in day, allow rest breaks
what is a key feature of how sx present in MG
sx (esp ptosis) becomes more pronounced w fatigue as they get tired throughout the day
what are aggravating factors for MG
emotional stress
systemic illness
thyroid d/o
pregnancy
menstrual cycle
inc body temp
meds
what meds can be aggravating factors in MG and why
ms relaxants
- dec strength of contractions, exacerbates
milk of magnesia
- related to substances in ms contraction (mg)
local anesthetics
some antibiotics
what is the most common and primary sx in MG at time of dx
ocular sx
what is the course of MG
fluctuating, overall progressive
- periods of active and inactive states
progression from ocular to generalized sx w/i 2yr period
diurnal changes - sx worse at night
nadir w/i 1-3yrs of onset
what is the average length of remission if pt w MG were to go into remission
5yr
what is the prognosis for someone w MG
good
- not rapidly progressive or fatal in most people
- better outcomes if dx early and treated early
how is MG severity related to antibody testing
inc severity in seropositive MG
- but better px w early thymectomy (thymus tumors or hyperplasia often removed)
- thymectomy benefit may dec w age of onset
how does px vary between thymoma and non-thymoma MG
similar severity and outcomes
sorry trick question mamas
what is the main source of mortality in MG
myasthenic crisis
- acute, severe flare
- more common in women
- cause respiratory failure
- rare
what are medical management options for MG
cholinesterase inhibitors
thymectomy
corticosteroids
immunosuppressants
plasma exchange and IVIg
how does cholinesterase inhibitors work to manage MG
prevent degradation of ACh
- can’t help w binding site so inc level of ACh in NMJ so that more ACh is available and circulating
typical outcomes for ocular MG
low disability rate
respond well to drug therapy
high rate of spontaneous remission
what are side effects of cholinesterase inhibitors
abdominal cramps
diarrhea
excessive saliva production
usually not severe or troublesome enough for people to go off meds
who is a thymectomy contraindicated in for MG
children
who is a thymectomy controversial in for MG
ocular MG
- if ocular only sx, rare to prescribe this surgery
when will you see the best outcomes from a thymectomy in MG
people <60yo
early in dz process
what are typical outcomes for a thymectomy in MG
70-80% have inc strength or dec need for meds
- remission rate of 33-38% but not immediate
why are corticosteroids used in medical management of MG
dec autoantibody synthesis
anti-inflammatory effects
what types of medical management strategies are more short term / for an acute crisis in MG
corticosteroids
immunosuppressants
plasma exchange and IVIg
would want to switch to other meds after (cholinesterase inhibitors)
what are SE of corticosteroids in MG
OP
wt gain
high BP
GI disturbances
want to avoid taking these long term
why are immunosuppressants used in management of MG
lessen autoimmune attack
what is a risk w the use of immunosuppressants in managing MG
inc risk of infection
what is the efficacy of plasma exchange and IVIg in managing MG
fast acting and effective
- but temp effects
more effective if combined w drug therapy
what PT intervention is indicated to prevent/dec severity of a myasthenia crisis
inspiratory ms training
what does evidence say ab PT and MG
lack of evidence to support specific interventions
what are PT strategies for MG
breathing exercises
submax resistive therex w low reps
aerobic exercise
what are the goals/purposes of PT in MG
PT = minimize effects
prevent disuse atrophy
focus on function/participate
goal is to educate people on need for frequent rest periods and pacing as sx worsen w repetitive use and w day
