A retrospective Canadian study of 80 people with double-seronegative myasthenia for anti-RACh and anti-MuSK antibodies, compared with 73 people with myasthenia for anti-RACh antibodies, showed that :
- the initial proportion of people with ocular forms (46.3%) was significantly higher in the double-seronegative group than in the anti-RACh myasthenia group;
- the Myasthenia Gravis Impairment Index (MGII) and simple single question (SSQ) scores at diagnosis were not significantly different between the two groups;
- they improved under treatment with an average follow-up of 42.8 months (from 8 to 90 months), although the improvement in the myasthenia gravis group with anti-RACh was significantly better;
- at the last check-up, 23% of double seronegative patients had ocular disease only.
