This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S., Subject name: Medicine
Investigation of choice for myasthenia gravis? 
Select and explain. 
A. Single Fiber E.M.G, B. Muscle biopsy, C. Nerve conduction velocity, D. Anti -acetylcholine receptor antibody
A: Single Fiber E.M.G
Answer: A: Single Fiber E.M.G 
Explanation: Ans. (a) Single Fiber E.M.GRef: Harrison 19th ed. / 442e-6* Single fiber E.M.G is the investigation of choice for myasthenia gravis and shows a decremental response* Anti-acetylcholine receptor blocking antibody TITER is the most specific test for diagnosis of myasthenia gravis. Also remember that Tensilon test is a screening test for myasthenia gravis. False positive tensilon test can be seen in motor neuron disease.