Table of Contents
Ocular Myasthenia Gravis
Clinical Features
Diagnostic Tests
Antibody Tests
Other tests
Ocular Myasthenia Gravis
Clinical Features
Triad: Ptosis, Oculomotor paresis and Obicularis oculi weakness
Ptosis
may be unilateral or bilateral
Alternating ptosis is specific for this condition
Eyelid fatigue
Ptosis worsens with prolonged upgaze or upon return to primary gaze
Cogan's lid twitch
After brief but sustained downgaze, a saccade to primary gaze results in the eyelid quickly rising and falling (1 mm or more typically)
Eyelid Curtaining
When lifting the more ptotic eyelid, the contralateral eyelid will droop more because of Hering's law
Resting for 5 minutes with the eyes closed will cause improvement in ptosis
Strabismus that fluctuates or appears fatiguable
Any type of strabismus possible
prolonged or sustained gaze in the field of action of the affected muscle may show increasing paresis
Lagophthalmos is rare
attempt to open the eyelid against forced closue- if the eyelid can be opened it suggest obicularis weakness
Diagnostic Tests
Antibody Tests
Acetylcholine Receptor Antibody
sensitivity 50% in Ocular myasthenia vs 90% in Generalized myasthenia
The most specific test, no false positives have been reported
Muscle specific tyrosine kinase antibodies (MuSK)
Rare cares of this antibody present in the setting of ocular myathenia without acetylcholine receptor antibodies
LRP4 antibodies
3 cases reported these present in setting of ocular myasthenia
Other tests
Ice Pack Test
Place a bag of ice on the ptotic lid for 1 minute
Immediately asses ptosis when ice removed
improvement is transient (<1 min)
sensitivity 80% if prominent ptosis present
Tensilon test
Edrophonium- inhibits acetylcholinesterase
transiently reverses muscle weakness
Sensitivity 85-95%
Electrophysiology
Repetitive nerve stimlation- reduction in amplitudes with repetitive stimulation
Single-fiber EMG- temoral variability of adjacent motor nerve fibers known as “jitter”.