Ocular Myasthenia Gravis following strabismus surgery and presenting as refractory strabismus

Ocular myasthenia gravis is a protean disorder and can present with myriad disorders of ocular motility. The diagnosis may not be obvious at presentation and strabismus surgery has occasionally been performed with unexpected outcomes. Strabismus surgery can be performed on patients with ocular myasthenia gravis who have stable ocular deviations, although outcomes may vary.

We report two patients who were operated for strabismus and were diagnosed as ocular myasthenia gravis later, when classic signs appeared. The first patient underwent right medial rectus recession and left lateral rectus plication for a left sixth nerve palsy surgery. He developed recurrent strabismus and ptosis 3 months after surgery and was diagnosed as ocular myasthenia gravis on the basis of positive ice test, fatigue test and repetitive nerve stimulation test. He was started on a tapering regime of oral steroids and pyridostigmine. This reduced the deviations to a level correctable by prisms eventually becoming orthophoric in primary position. The second patient had a severe undercorrection of strabismus after large recess resect procedure on the right eye for large angle exotropia. Five months after surgery, he presented with right eye ptosis and a recurrence of strabismus. He tested positive for anti-acetylcholine receptor antibodies. The ptosis improved with oral steroids and pyridostigmine and he eventually went into a natural remission. The ocular deviation, however, remained unchanged.

The emergence of ocular myasthenia in patients undergoing strabismus surgery is a rare occurrence but should be suspected in patients with unexpected outcomes after strabismus surgery.