Generalisation in myasthenia gravis presenting with pure ocular symptoms

Abstract

INTRODUCTION: Myasthenia gravis (MG) is an autoimmune disorder characterised by impaired skeletal muscle neuromuscular transmission mediated by anti-acetylcholine receptor autoantibodies (AChRAb) in the majority of patients. Factors that determine generalisation in MG patients who have clinically restricted extraocular involvement at onset are uncertain. METHODS: Records of MG patients followed up in our neurology clinic were reviewed. Patients who had MG clinically restricted to extraocular muscles on initial presentation were studied. Classification and outcome were assessed according to Myasthenia Gravis Foundation of America (MGFA) 2001 recommendations. RESULTS: A total of 31 patients presenting with pure ocular symptoms at clinical onset were studied. Twenty patients (65%) were female with a mean follow-up duration of 92 months (range, 5-480 months). Among them, seven (22%) subsequently developed generalised MG at a mean age of 53.9 years (range, 23-72 years). The mean disease duration at generalisation was 48 months (range, 3-121 months). Four of these seven patients had thymectomy performed; two had reactive lymphofollicular hyperplasia, one thymoma, and one thymic lymphoepithelial carcinoma. Four patients continued to require cholinesterase inhibitors and immunosuppressants (MGFA post-intervention status [PIS] MM-3); two on low-dose cholinesterase inhibitor only (MM-2) and one required no pharmacological treatment in the past year (MM-0). There was no difference in onset age, sex, duration of follow-up, acetylcholine receptor antibodies and striated muscle antibodies seropositivity rates, electrophysiological findings between patients who developed generalised MG and patients who did not. Patients who subsequently developed generalised MG had a higher frequency of thymoma (defined by CT scan or histology) than those who did not (43% vs 8%, P=0.029). As expected, patients who developed generalised MG were more likely to be treated with immunosuppressants (57% vs 29%, P=0.033) and thymectomy (57% vs 4%, P=0.007) than patients who did not. CONCLUSION: Presence of thymoma in MG patients who had disease clinically restricted to extraocular muscles on initial presentation is associated with a higher risk of subsequent MG generalisation.