-Myasthenia gravis is a post synaptic autoimmune disorder due to failure of neuromuscular transmission resulting from binding of autoantibodies to proteins involved in signalling at the NMJ.
-OMG is where weakness is clinically isolated to the periocular muscles (extraocular muscles, LPS and orbicularis oculi).
- Ocular muscles are involved in 97% of patients during disease.
FEATURES:
-Ptosis.
-Diplopia.
-Fluttering of ptotic eyelid observed during eye movements (Lid Hopping)
-Cogan's lid twitch: Quick overshooting upward movement followed by a down-drift of the upper lid after the patient performs a saccade back to primary position from looking down.
-Peek Sign: On prolonged forceful closure of the eyes , they drift open to reveal sclera or cornea in spite of the patient's attempt at keeping them closed.
-Simpson's sign: Provocative tests with looking upward or to one side for 60 seconds gives clue to diagnosis.
DIAGNOSIS:
-Sleep Test.
-Ice Pack Test.
-Edrophonium/Neostigmine test.
WHAT IS THE MECHANISM OF ACTION IN ICE-PACK TEST?
-Icepack is placed over the patient's closed eyelids for 2minutes.
-The test is considered positive when the upper eyelid elevates by atleast 2mm following application of ice.
-Cooling reduces acetylcholine esterase activity which increases the amount of available ACh available at the NMJ.
-This promotes the efficiency of ACh in eliciting depolarization at the motor end plate.
TREATMENT:
-Acetylcholinesterase inhibitors.
-Corticosteroids.
-Other immunomodulators.
-Plasma exchange (Plasmapheresis) and IV Immunoglobulins.
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Image from Rajan Eye Care Hospital