Myasthenia Gravis Flashcards
(44 cards)
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
