Two cases of thymoma-associated myasthenia gravis without antibodies to the acetylcholine receptor

Thymoma-associated myasthenia gravis is considered a more severe disease compared with non-thymomatous myasthenia gravis and is generally associated with antibodies to the acetylcholine receptor (AChR-Ab). Even though a single case of thymoma-associated myasthenia gravis with anti-muscle specific kinase (MuSK) antibodies has been reported, to our knowledge, seronegative thymoma-associated myasthenia gravis has not been described. We report on two cases of this disease without antibodies to AChR or MuSK as a further evidence of the variability of myasthenia gravis in terms of antibody profile and thymic pathological findings.