Objective: The frequency of ocular myasthenia gravis (OMG) in patients referred to an academic neuro-ophthalmology clinic for suspected myasthenia gravis is not known. Our objective was to determine the frequency of ocular OMG in patients referred to an academic neuro-ophthalmologist and determine alternate diagnoses and response to therapy.
Methods: We performed a retrospective chart review of patients presenting to the University of Kansas Neuro-Ophthalmology Clinic with suspected OMG over 9 years. We defined OMG as isolated ptosis/diplopia at initial presentation supported by at least one of the following abnormal tests: edrophonium test, ice test, Cogan lid twitch, fatigability on sustained upgaze, acetylcholine receptor binding antibody, greater than 10% decrement on repetitive stimulation, or abnormal single-fiber jitter. We also determined the cause of ptosis/diplopia if it was not the result of OMG. Patients who progressed from OMG to generalized disease were termed transformed myasthenia gravis (TMG).
Results: One hundred thirty-eight patients were referred with mean age at presentation 58 ± 19 years. Myasthenia gravis was diagnosed in 101 patients; 95 had OMG; six had generalized MG. Diagnosis in the other 37 was cranial nerve palsies (nine), levator dehiscence (five), multiple sclerosis (two), blepharospasm (two), decompensated phorias (three), accommodation spasm (four), exophoria (three), skew deviation (two), Graves disease (one), hypertropia (one), myopathy (one), neurosarcoidosis (one), progressive supranuclear palsy (one), Miller Fisher variant of Guillain-Barre syndrome (one), and obstructive sleep apnea (one). Mean follow-up was 3.0 ± 2.8 years. Test sensitivity/specificity in OMG was fatigability on sustained upgaze 0.80/0.63; ice pack 0.80/0.25; Cogan lid twitch 0.59/1.00; edrophonium 0.88/0.50; acetylcholine receptor binding antibody 0.38/1.00; repetitive nerve stimulation 0.24/1.00; and single-fiber electromyography 0.90/1.00. Pyridostigmine was used without prednisone in 59 of 97 patients with OMG and 12 of 59 developed TMG. Prednisone was used in 38 patients; 21 of 38 (55%) met Myasthenia Gravis Foundation of America improvement status and none had TMG.
Conclusion: The diagnosis of myasthenia gravis was confirmed in the majority of patients referred to our academic neuro-ophthalmology clinic, but 27% did not have myasthenia gravis. It is possible that prednisone treatment of OMG may prevent progression to TMG, but further study is required.