Pseudo-myasthenia gravis and thymic hyperplasia in Graves' disease

Background: Diagnostic confusion between thyroid disease and myasthenia gra vis (MG) can arise because the two may have similar clinical features, and also because of the more frequent coexistence of these autoimmune disorders in the same individual. In MG, autoantibodies directed against the acetylc holine receptor result in muscle weakness. Thymic pathology is well recogni zed in MG, with thymic hyperplasia frequent in early onset MG and thymoma m ore common in later onset MG. In Graves' disease, autoantibodies against th yroid antigens result in hyperthyroidism. A seldom-recognized feature of Gr ave's disease is the occurrence of an enlarged thymus (thymic hyperplasia) on chest CT, or of thymic lymphoid hyperplasia pathologically. Case study: This report describes a case in which the discovery of a mediastinal mass d uring imaging of the thyroid, and the presence of myasthenic-like symptoms, in a patient with Graves' disease prompted investigations into whether the patient also had MG. Results: Despite symptoms which strongly suggested MG , subsequent investigations did not confirm the diagnosis, and treatment of Grave's lead to a resolution of the symptoms and regression of the thymic enlargement seen on CT. Conclusions: The case study highlighted clinical si milarities between Grave's disease and myasthenia gravis which might cause diagnostic confusion, and also the investigations which are useful in order to differentiate the two diseases. In addition to common clinical features , the autoimmune diseases Grave's disease and myasthenia gravis may both pr oduce radiological thymic enlargement.