title: Pseudo-myasthenia gravis and thymic hyperplasia in Graves' disease.
abstract: BACKGROUND
  Diagnostic confusion between thyroid disease and myasthenia gravis (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 acetylcholine receptor result in muscle weakness. Thymic pathology is well recognized in MG, with thymic hyperplasia frequent in early onset MG and thymoma more common in later onset MG. In Graves' disease, autoantibodies against thyroid antigens result in hyperthyroidism. A seldom-recognized feature of Grave's disease is the occurrence of an enlarged thymus (thymic hyperplasia) on chest CT, or of thymic lymphoid hyperplasia pathologically.
  
  
  METHODS
  This report describes a case in which the discovery of a mediastinal mass during 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 similarities 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 produce radiological thymic enlargement.
authors.affiliation: Department of Clinical Neurological Sciences, University of Western Ontario, London Health Sciences Centre, Canada.
authors.forename: M W
authors.initials: MW
authors.lastname: Nicolle
mesh_terms: D000328:Adult; D014151:Anti-Anxiety Agents / Q000627:therapeutic use; D000893:Anti-Inflammatory Agents / Q000627:therapeutic use; D013956:Antithyroid Agents / Q000627:therapeutic use; D003937:Diagnosis, Differential; D005260:Female; D006111:Graves Disease / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy; D006801:Humans; D008713:Methimazole / Q000627:therapeutic use; D009157:Myasthenia Gravis / Q000097:blood / Q000175:diagnosis*; D011241:Prednisone / Q000627:therapeutic use; D011433:Propranolol / Q000627:therapeutic use; D011859:Radiography; D013952:Thymus Hyperplasia / Q000097:blood / Q000000981:diagnostic imaging* / Q000188:drug therapy; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D014151:Anti-Anxiety Agents; D000893:Anti-Inflammatory Agents; D013956:Antithyroid Agents; D008713:Methimazole; D013972:Thyrotropin; D011433:Propranolol; D013974:Thyroxine; D011241:Prednisone