Acetylcholine receptor antibody positivity rate in ocular myasthenia gravis: a matter of age?

Background: Anti-acetylcholine receptor antibodies (AChR Abs) are detected in 85% of myasthenia gravis (MG) patients, at higher rates in patients with late-onset disease. AChR Ab frequency is generally thought to be much lower in ocular MG (OMG), although recent studies reported positivity rates higher than 70%. We hypothesized that the improved AChR Ab diagnostic yield in OMG could be related to an increased frequency of late-onset disease, as observed in generalized MG. Methods: We compared OMG patients, with disease onset before or after 1998, for the age of onset, sex, presence of thymoma, immunosuppressive therapy rate, AChR Ab positivity, and follow-up duration. All patients had a follow-up ≥ 2 years. AChR Abs were tested by radioimmunoassay. Results: The study included 133 patients. Disease onset occurred before 1998 in 54/133 cases (41%). Age of onset, the proportion of late-onset patients, and AChR Ab positivity rate were significantly increased in the more recent population. Thymoma frequency was similar in the two series. On multivariate analysis, the only variable predicting AChR Ab positivity was the age at onset ≥ 50 years (OR = 6.50, 95% CI = 2.70–15.63, p < 0.0001). Conclusions: Our results confirm that current AChR Ab positivity in OMG may be higher than generally thought. In our population, this finding was associated with an increased frequency of late-onset cases.