Age of onset and factors affecting treatment responses in ocular myasthenia gravis.

Background: Ocular myasthenia gravis (OMG) is an autoimmune disease which causes ptosis, diplopia, or both. It can be categorized as early or late onset, with differing presenting characteristics and prognoses. Currently, there is limited information available to compare characteristics and outcomes in onset groups in Thailand.

Objective: To describe and compare baseline characteristics and outcomes in OMG patients classified by onset groups and to investigate the factors associated with the disease, especially in terms of treatment responses classified according to the MGFA Post-Intervention Status (MGFA-PIS).

Methods: OMG patients diagnosed between January 2014 and March 2021 at Rajavithi Hospital, Thailand, were categorized into 2 groups based on age of onset, and baseline characteristics were analyzed and compared. The treatment responses of each group in terms of time to achievement of minimal manifestations (MM) were analyzed.

Results: Eighty-one patients (38 with early and 43 with late onset) were included, and the mean (SD) follow-up time was 35.85 months (17.25). There was no significant difference between the baseline characteristics of the two groups. A low dose of pyridostigmine was more commonly used in the early-onset group (p = 0.01), while the mean dose of corticosteroids was significantly lower in the late-onset patients (p < 0.001). We found that seropositivity of acetylcholine receptor antibody decreased the odds ratio of achievement of MM (OR 0.185, 95% CI 0.043-0.789, p = 0.023) and receiving a high dose of pyridostigmine (≥ 120 mg/day) increased the odds ratio of achieving it (OR 8.296, 95% CI 2.136-32.226, p = 0.002).

Conclusions: A higher dose of pyridostigmine may be necessary for achievement of favorable treatment response. AChRAb seropositivity is a predictor for unfavorable treatment response in Thai populations.