Mediastinal MRIs are indicated in all patients who are diagnosed with myasthenia gravis, and this is because 10% of myasthenia patients have thymomas (tumours of the thymus). These are mostly benign, but even in this state they can cause problems due to compression of adjacent structures:
- superior vena cava superior vena cava syndrome
- oesophagus dysphagia
- trachea dyspnoea, cough
Some, however, are malignant.
Even in the absence of a thymoma, 85% of patients clinically improve after thymectomy (the reason for this isn't clear), and so many authorities recommend routinely removing it in all patients with generalised myasthenia gravis if you're anywhere between a teenager and 55 years old.