Several predictors for conversion from ocular myasthenia gravis (OMG) to generalized myasthenia gravis (GMG) were identified in a recent article published in the Orphanet Journal of Rare Diseases.
Patients who had repetitive nerve stimulation (RNS)-positivity, defined as a decrement of more than 10% on RNS at 3 Hz, and those with histotype B2/B3 thymoma were found to be at a higher risk of conversion. In contrast, patients who had thymic hyperplasia and stage I thymoma had a greater chance of complete stable remission (CSR).
“We revealed the impact of thymus pathology and thymoma anatomical features on prognosis of OMG after thymectomy,” the authors said.
“Our retrospective study showed that RNS-positivity and World Health Organization (WHO) subtype B2/B3 thymomas were significantly associated with post-thymectomy OMG conversion. On the other hand, thymic hyperplasia and Masaoka–Koga Stage I thymoma were independently associated with post-thymectomy OMG CSR,” the authors continued.
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Among patients with RNS-positivity, 84.6% converted to GMG, compared to only 35.6% of patients who were not RNS-positive (P =.002). Patients with histological subtype B2/B3 thymoma were at an increased risk of conversion in comparison to patients with either hyperplasia or subtype AB/B1 thymoma (P =.002). Acetylcholine receptor antibody (AchR Ab)-seropositivity showed a trend for increased risk of conversion but it did not reach significance (P =.085).
When looking at the chance of achieving CSR, patients with thymic hyperplasia or stage I thymoma had a higher chance than those with stage II/III (P =.001). AchR Ab-seropositivity significantly reduced the chance of achieving CSR (P =.029) and RNS-positivity showed a trend toward a reduced chance of CSR (P =.063).
Patients who achieved CSR also had significantly longer follow-up times (78.3 ± 28.6 vs 58.3 ± 25.4 months; P =0.015), indicating that more patients may have achieved CSR during a study with a longer follow-up time.
Univariate and multivariate analyses using Cox proportional hazard modeling verified the predictive nature of the above-mentioned factors for OMG conversion and CSR.
A total of 58 OMG patients were included in the study with 13 (22.4%) developing GMG at the time of the last review. Conversion occurred a median of 9.2 months after thymectomy and 12.7 months after symptom onset. Conversion occurred in 11 of the 13 patients within 2 years of symptom onset.
Reference
Zhang J, Zhang Z, Zhang H, et al. Thymectomy in ocular myasthenia gravis-prognosis and risk factors analysis. Orphanet J Rare Dis. 2022;17(1):309. doi:10.1186/s13023-022-02454-y
