Which of the following is the most sensitive test for the diagnosis of myasthenia gravis?

Myasthenia gravis is a neuromuscular disorder, due to decrease in the number of acetylcholine receptors at the neuromuscular junction secondary to an antibody mediated autoimmune attack. It is characterized by weakness and fatigability of skeletal muscles. It can be diagnosed by the increase in muscle strength following administration of anticholinesterase drug. Most sensitive test in diagnosing myasthenia is edrophonium test. In this test, after administration of edrophonium, muscle strength improves and lasts for 5 minutes. Ref: Harrison's Internal Medicine, 18th Edition, Chapter 386; Clinical Neurology By Roger P. Simon, 7th Edition, Chapter 5