The diagnosis of myasthenia gravis is made by a positive edrophonium test, repetitive nerve stimulation test of a weak muscle, and anti-acetylcholine receptor antibody assay. MRI of the mediastinum is now indicated to:

Ans. B. Rule out thymomaTen percent of myasthenia patients have thymic tumors. Surgical removal of all thymoma is necessary because of local tumor spread. Even in the absence of tumor, 85% of patients clinically improve after thymectomy. It is now consensus that thymectomy be performed in all patients with generalized MG who are between puberty and age 55. Sarcoidosis causes peripheral neuropathy and aseptic meningitis, but not a myasthenia syndrome. Small cell carcinoma is associated with Lambert-Eaton syndrome, a paraneoplastic syndrome similar to myasthenia. In Lambert-Eaton syndrome, an autoimmune response results in anti-calcium channel antibodies A chest x-ray would be sufficient to screen for malignancy or infection.