What is the role of imaging studies in the evaluation of myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

On plain anteroposterior and lateral views, radiography may identify a thymoma as an anterior mediastinal mass. A negative chest radiograph does not rule out a smaller thymoma, in which case a chest computed tomography (CT) scan is required. Chest CT scan should be obtained to identify or rule out thymoma or thymic enlargement in all cases of MG (see the images below). This is especially true in older individuals.

CT scan of chest and mediastinum showing thymoma i CT scan of chest and mediastinum showing thymoma in patient with myasthenia gravis.
CT scan of chest showing an anterior mediastinal m CT scan of chest showing an anterior mediastinal mass (thymoma) in a patient with myasthenia gravis.

It is essential to rule out mass lesions compressing the cranial nerves in strictly ocular MG. CT or preferably magnetic resonance imaging (MRI) of the brain and orbit is indicated. It is helpful when the diagnosis of MG is not established and to rule out other causes of cranial nerve deficits. MRI can evaluate for intraorbital or intracranial lesions, basal meningeal pathology, or multiple sclerosis.


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