Ocular Myasthenia gravis: determining the predictive factors of secondary generalisation

Introduction

Myasthenia gravis (MG) can be classified according to clinical features into ocular MG (OMG) and generalised MG (GMG). However, OMG carries the risk of conversion to GMG. In this study, we aimed to determine the predictive factors for the secondary generalisation of OMG patients.

Methods

OMG patients followed-up in our hospital from January 1999 to November 2023 were retrospectively reviewed. Demographic and clinical characteristics data were collected from medical records. OMG patients with follow-up of < 2 years were excluded.

Results

Of the 122 patients included, 87 (71.3%) remained as OMG and 35 (28.7%) had converted to GMG. The median time taken for generalisation was 12 months (IQR 6–30). 73.5% of patients had converted to GMG within 2 years. In univariate analysis, a significantly higher proportion of patients with positive anti-AChR antibodies (94.1% vs. 67.1%, p = 0.002), higher antibody titre (8.0 vs. 1.6 nmol/L, p < 0.001), positive repetitive nerve stimulation (RNS) (54.5% vs. 15.9%, p < 0.001), positive single-fibre electromyography (96.7% vs. 76.0%, p = 0.013) and the presence of thymic abnormalities (35.3% vs. 3.5%, p < 0.001), specifically thymoma (29.4% vs. 1.2%, p < 0.001) were associated with secondary generalisation. Conversely, higher percentage of patients who were treated with corticosteroid remained as OMG (37.9% vs. 17.1%, p = 0.026). However, in multivariate analysis, only positive anti-AChR antibodies (OR_adj 9.6, 95% CI 1.7–56.1), positive RNS (OR_adj 4.0, 95% CI 1.3–12.5) and the presence of thymoma (OR_adj 29.5, 95% CI 2.5-351.1) were independently associated with secondary generalisation.

Conclusion

The presence of anti-AChR antibodies and thymoma with positive RNS were the predictive factors of secondary generalisation in OMG.