Association between acetylcholine receptor characteristics in biceps motor endplates and the epidemiological predictors for conversion from ocular to generalized myasthenia gravis
Objective: Epidemiological studies have identified various predictors of conversion from ocular myasthenia gravis (OMG) to secondary generalized myasthenia gravis (SGMG), but none have been confirmed. We investigated the effects of the epidemiological conversion predictors on the destruction of motor endplates in the biceps of patients with OMG and attempted to identify predictors of conversion to SGMG histologically.Methods: Patients with clinically diagnosed OMG who requested immunohistological diagnosis and who underwent muscle biopsy were included in this study. We immunostained the biceps motor endplate and semi-quantitatively measured the density and number of AChRs to determine their association with the epidemiological predictors of conversion from OMG to SGMG.Results: Thirteen patients with OMG were included, of which two patients with positive AChR antibody and concomitant thymoma converted to SGMG. In the classification according to the presence of AChR antibody, the AChR densities tended to be lower in the antibody-positive group than in the negative group (p=0.079), and the AChR numbers were significantly lesser in the AChR antibody-positive group than in the negative group (p=0.019). There were no differences in AChR densities or numbers according to sex, presence of thymic abnormalities, or presence of comorbid autoimmune diseases.Conclusion: In OMG, the AChR numbers in motor endplates of the biceps were significantly lesser in the AChR antibodypositive group than in the negative group. Since the muscle strength tends to decrease as the number of AChRs decreases, AChR antibody positivity may be a predictor of OMG to SGMG conversion, but further studies are needed to confirm
