What is the next step in evaluating a patient suspected of having Myasthenia Gravis?

In the evaluation of a patient suspected of having Myasthenia Gravis (MG), the most appropriate next step is to test for serum acetylcholine receptor antibodies. This test helps to confirm the diagnosis, as the majority of patients with MG have antibodies that bind to acetylcholine receptors, leading to the characteristic muscle weakness.

While imaging studies, such as a CT scan of the chest, can be important for assessing the presence of thymoma (a tumor associated with MG), they are not considered the first-line test for making the diagnosis. The focus is typically on confirming the presence of the disease through antibody testing and clinical assessment of symptoms.

In contrast, electromyography (EMG) can also show a decremental response in muscle strength, indicating MG; however, it is often used after antibody testing or in conjunction with it for further confirmation. Cerebral MRI is not relevant in the context of diagnosing MG as it does not provide the necessary information about the neuromuscular junction or the presence of autoimmune markers.

Therefore, the serum acetylcholine receptor antibody test is the most direct and informative initial step in the diagnostic workup for Myasthenia Gravis.