Which diagnostic method is used to confirm the presence of myasthenia gravis?

The edrophonium challenge test is a key diagnostic method for confirming the presence of myasthenia gravis. This test involves the administration of edrophonium chloride, a short-acting acetylcholinesterase inhibitor. When patients with myasthenia gravis are given edrophonium, they typically demonstrate a temporary improvement in muscle strength. This response is due to increased availability of acetylcholine at the neuromuscular junction, compensating for the reduced effectiveness of acetylcholine caused by the antibodies that target acetylcholine receptors. Consequently, the positive response to this test is indicative of myasthenia gravis.

While the blood test for acetylcholine receptor antibodies is also used to support the diagnosis of myasthenia gravis, it is primarily a confirmatory test rather than a direct assessment of muscle function. Electromyography can help characterize the neuromuscular transmission but does not provide the direct evidence of the condition that the edrophonium challenge test does. X-ray analysis is not relevant in the diagnosis of myasthenia gravis, as it is primarily used for imaging purposes unrelated to this neuromuscular disorder.