Myasthenia Gravis

• autoimmune disorder in which antibodies prevent the neurotransmitter acetylcholine from attaching to muscle receptors, thereby interfering with muscle contractions
• characterized by fatigability of voluntary eye movements (diplopia worsens as day progresses, improves with sleep)
• can present with diplopia, ptosis or both

Tests

• sustained upgaze: patients will show a gradual worsening as the levator muscle fatigues
• ice pack test: apply a cold pack to the eyelid for 5 minutes (cold temp allows Ach to have more time to react with the muscle receptors), check for improvement in ptosis
• sleep test: have the patietn take a nap in the exam chair for 30-45 minutes, check for improvement in ptosis
• Tensilon is an IV cholinergic drug that typically shows improvement in muscle function within seconds

Treatment

• Mestinon (cholinergic drug) and immunosuppresive therapy (neurophthalmology)
• if medications don't eliminate ptosis/diplopia, may try prismatic corrections and ptosis crutches

Differentials

• 3rd nerve palsy: has vertical and horizontal component
• skew deviation: usually appears with concomitant hypertropia and other abnormal eye movements such as nystagmus
• disease of the orbit: neoplastic, inflammatory, infectious, traumatic can cause proptosis, lid retraction, periorbital edema, conjunctival hyperemia, disc edema