I do this all the time when I feel something is just not 'right' or i feel a rather significant neuro change in my condition.most docs,if you can explain to them just why you feel this particular test is actually needed ,will in most cases agree to it.if they get a bit icky about it,stand your ground and just be prepared to back up your request with the reasons why you feel this test needs to be done.when dealing with any docs,espescially "specialists" you need to advocate for yourself in order to get the best possible treatment.most neuros just love to send people for 'tests" so I would thing that this would not be a major problem for you really.As long as you can justify the need for the test,you should not have a big problem.hope all goes well for you,Marcia