Pearls on antibody testing in MG

1. AchR antibody is positive in 80-85 % of patients with MG, but only 55 % of pure ocular disease
2. Less than one percent of patients have pure blocking antibodies (others may have associated with binding antibodies) and so blocking antibodies are of little clinical use.
3. Modulating antibodies cross link the receptor and modulate their rate of degradation. It is most helpful as a test when the level of binding antibody is negative which is 3-4 %.
4. High levels of modulating antibodies, like anti striated muscle antibodies, occur in association with lymphoma, although can occur sporadically too especially in old.
5. MuSK antibody, important in clustering of receptors in NMJ, are positive in 40 % of AchR negative patients, only occassionally in those with pure ocular disease.