A 25 year old female presents with generalized restriction of eye movement in all direction, intermittent ptosis, proximal muscle weakness and fatigability.Which is the MOST useful test in making the diagnosis?

This patient is showing signs and symptoms of Myasthenia gravis. Edrophonium test is the most useful test in making a diagnosis of this condition because of the rapid onset and sho duration of its effect. This test is considered to be positive if there is any improvement in the weakness of this patient after administration of edrophonium. Other diagnostic tests used for diagnosing myasthenia gravis are: Acetyl choline receptor antibodies: Presence of this antibodies is viually diagnostic of MG, but a negative test does not exclude the disease. Rapid nerve stimulation test: In this test electric shocks are delivered at a rate of 2 or 3 per second to the appropriate nerves, and action potentials are recorded from the muscles. In these patients there is a rapid reduction of >10-15% in the amplitude of the evoked responses. Ref: Drachman D.B. (2012). Chapter 386. Myasthenia Gravis and Other Diseases of the Neuromuscular Junction. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.