Introduction The aim of our study was to establish if there were any clinical and immunological differences between early (EOMG) and late onset myasthenia gravis (LOMG).

Methods and results We recruited 150 patients with myasthenia gravis making this the largest prospective cohort study in MG to date. Most (74%) patients have LOMG. Of these, 8 (5.33%) are seronegative. Most (88%) are positive for AChR Abs, 4% have MuSK, 2% LRP4 and 10% are double positive to AChR and MuSK Ab on CBA.

The incidence of LOMG is higher than EOMG. There is a statistically significant fall in AChR titre levels on serial measurement (p <0.0001). LOMG pts have higher AChR titres at recruitment compared to EOMG (p=0.0498) with higher MG composite scores (p=0.0287). Significantly higher numbers of LOMG pts are positive for AChR Ab on RIA in generalised MG compared to EOMG. A third of the pts with Early Onset Generalised MG are positive for MuSK Abs on CBA. There is no significant difference in clinical presentation between single seropositive pts Vs double seropositive pts. AChR Ab titres are lower in ocular EOMG versus ocular LOMG and titres in ocular patients are lower than in generalised patients.Flow cytometric analysis of PBMCs showed a significantly reduced percentage of Treg cells in our patient cohort compared to healthy controls (p<0.0001) and a significant difference in the levels of TNFa, IL10 and IL17 produced.

Conclusion Our study has shown that there are clinical and immunological differences between early onset and late onset myasthenia gravis, both respond well to treatment with an improvement in composite scores and a fall in antibody titres. We are continuing to study this cohort of MG patients with extended follow-up.