Factors affecting the progression from ocular to generalized myasthenia gravis

Abstract

Objective To explore the clinical manifestation of secondary generalized myasthenia gravis(GMG) and analyze the factors affecting the progression from ocular myasthenia gravis(OMG) to GMG. Methods This research constitutes a single-center, retrospectively-collected prospective cohort study. We comprehensively reviewed our self-managed myasthenia gravis(MG) database drawn from personal clinical experience from January 2000 to June 2013. Patients underwent series of examination including repetitive nerve stimulation (RNS) tests, measurement of serum acetylcholine receptors antibody and serum muscle-specific tyrosine kinase antibodies, thymus computer tomography scan etc. Patients were treated with pyridostigmine bromide, corticosteroid therapy and (or) thymectomy based on a non-randomization pattern and they were documented for their respective symptoms of OMG and GMG and date of GMG conversion. Logistic regression analysis was adopted to determine the influencing factors correlated with the development of GMG during the follow-up. Results Totally 770 patients initially diagnosed with OMG were included, among whom 573(74%) patients remained with OMG (R-OMG group) and 197(26%) patients developed into GMG (GMG group) during the follow-up. (1) In comparison with their R-OMG counterparts, patients with secondary GMG were older at onset; Displayed more frequent RNS abnormality of facial nerve, accessory nerve and ulnar nerve; Showed higher incidence of thymoma and were less treated by early corticosteroids. (2) For GMG group, 81%(160/197) of them displayed bulbar MG; 67%(132/197) of GMG conversion occurred within 2 years, and 84%(166/197) within 5 years. In comparison with the patients with onset of “≤14-year-old”, both of patients with “15—49-year-old” and “≥50-year-old” displayed higher conversion rate and shorter conversion duration (median: 10 years versus 1 year and 6.5 months). (3)RNS abnormality of accessory nerve（OR=6.650, 95%CI 3.547—12.471; P<0.05）and thymoma（OR=7.924, 95%CI 2.554—24.585; P<0.05） were prognostic factors for the development of GMG, while early corticosteroid（OR=0.232, 95%CI 0.119—0.452; P<0.05） predicted the reduction of the risk of generalization. Conclusions Multiple factors including abnormal RNS of proximal limb muscles, thymoma, early corticosteroids therapy and possibly even onset age of over 15-year-old may involve the generalization in patients with OMG at onset. Key words: Myasthenia gravis; Ophthalmoplegia; Thymoma; Prognosis