B6.036 Myasthenia Gravis

Question 1

test in suspected M.G patient with ptsosis

Answer 1

Tensilon Test
EMG
blood test for antibodies

Question 2

how does a tensilon test work

Answer 2

short acting AChE inhibitor
prolongs time that ACh can interact with AChR
improves neuromuscular transmission

Question 3

conclusion from tensilon test

Answer 3

not conclusive for MG

consistent with a defect in NMJ function though

Question 4

why would you not use tensilon test in all patients?

Answer 4

ACh is used at other synapses in body (particularly in sympathetic)
could cause cardiac issues
will cause increase in salivation and sweating

Question 5

epidemiology of MG

Answer 5

incidence is 3-4/10,000
females 2x males
female onset 2-3rd decade
male onset 5-th decade

Question 6

symptoms of MG

Answer 6

droopy eyelids
double vision
difficulty swallowing
symptoms worse at end of day
hypotonia

Question 7

EMG findings in MG

Answer 7

decrease in amplitude with repeated stimulation because fewer muscle fibers in motor unit are firing action potentials

Question 8

treatment for MG with AChR autoantibodies

Answer 8

cholinesterase inhibitors
thymectomy: permanent remission in majority
plasmapheresis: modest improvement, often used during acute respiratory MG
immunosuppresants

Question 9

other autoantibodies that can cause MG other than anti-AChR

Answer 9

anti-MuSK
anti-agrin
anti-LRP4

Question 10

why does thymectomy work for patient with AChR autoantibodies

Answer 10

high correlation between abnormal cell growth in thymus and presentation of MG
overgrowth of smooth muscle-oid cells in thymus make a lot of AChR
immune cells pick up on production and produce Abs against the AChRs

Question 11

what is Titan protein

Answer 11

largest protein in body
binds end of myosin thick filaments
can get leaked out into system with muscle damage
usually not exposed to immune system, so when it is leaked out, autoAbs develop
thus anti-Titan abs in MG

Question 12

what does MuSk do

Answer 12

keeps AChRs aggregated in NMJ

Question 13

can you do a thymectomy for anti-MuSK type MG?

Answer 13

no

thymus not involved in pathogenesis

Question 14

treatment options for anti-MuSK MG

Answer 14

strong immunosuppressants
Rituximab
MTX

Question 15

what can cause double muscle compound action potential in response to a single nerve stimulation

Answer 15

point mutation in B subunit of AChR

increased open channel time

Question 16

effects of increased open channel time

Answer 16

excess Ca2+ comes into muscle and stimulates proteases

proteases start destroying channel

Question 17

ttx for this condition

Answer 17

SSRIs (Prozac)

closes AChR faster