I think you proceed with your doctor's advice, and take the Avonex. And then call your doctor to confirm that you're on it, and ask about the very unprofessional actions of his nurse. She should not have called you, especially when she didn't have the rest of your records in front of her. The doctor's role is to see the whole story -- physical exam of the patient (you!), results of all the tests, his years of experiece -- all that -- go into a diagnosis, not the results of just one test.
I'm sorry you've encountered that sort of unprofessional behavior.
I know from experience that medical staff members in all kinds of positions may say, or have an opinion, but the only one that counts is the doctor or doctors that are working your case.
With my first MRI, came a report from the radiologist that said that there were no signs of MS and perhaps I had sustained a major blow to the head. I was confused and angry. I have never had a major blow to the head. (reading that report caused me more anxiety and made me feel worse) My Neuro put the set of pictures up on the white light board and went over each one with me. She pointed out that this particular radiologist must not have had any real experience with MS, as she circled the lesions and showed me the atrophy. Then she said there was no evidence anywhere of a major blow to my head.
When my LP came back negative, my Neuro's Secretary called and told me that "it was good news, no bands means no MS" Again, I had to wait until my appointment with my Neuro, and she calmly told me that "no bands on your LP doesn't mean squat" You have MS and that was to see how it has progressed. She was very upset at the secretary for calling me and telling me what she did.
Therefore, unless it is your doctor, talking to you face to face or on the phone, take everything else with some hesitancy. Don't be in a hurry to force a answer from someonethat is not your doctor. It is hard to wait, it is hard to deal with unknowns, and it is hard to deal with MS, but don't make your anxiety worse by getting opinions from any one except your physcian.