Which of the following is correct concerning the Edrophonium (Tensilon) test?

Which of the following is correct concerning the Edrophonium (Tensilon) test?

The onset of action is rapid, and the duration of maximal effect is short.

The effects last for 2-4 hours.

It is a useful test in diagnosing Guillain-Barr� syndrome.

All of the above"

The onset of action is rapid, and the duration of maximal effect is short.