Are you serious? I would get a second opinion too. ALS is something that is considered rare and I don't know how someone could diagnose you in 15 minutes with it. I don't know too much about ALS but I do know some time and extensive testing should be completed prior to making a diagnosis like that. My father's friend had it; his porgressed quickly but from the little I know it can progress quickly or slowly.
Secondly, they didn't tell you the results of any of your blood work, MRI of the brain, etc.? Strange. You can always requests copies of the results to take with you to Northwestern.
I don't know how fast you will get them. Also, you can check with the Neurologist that referred you Mayo to see if he/she got a copy of your test results that he can give to you.
I am sure your nerves are shot about all this; HANG IN THERE. Sounds like you have a family that supports you.
Hopefully, it will turn out not to be ALS. It is always good to get second opinion when a rare diagnosis is made even if Mayo had spent hours testing you.
Keep us posted.
About all I can comment about is concerning what records the Mayo Clinic might have had when they finally saw you and did their 15-minute exam. Normally, if you are referred to a place like that by a neurologist, your neuro had in his possession all sorts of records, tests, any pictures and reports of scans, a letter with lists of his thoughts and conclusions, and also your history. Those are ROUTINELY forwarded to your referral doc, which in your case is the Mayo Clinic. Therefore the Mayo people already knew a whole lot about you before they first walked in the room and met you. Of course, if your neuro had NO information to forward, disregard what I have said, and I'm glad you're getting a second opinion, because if nothing else, you should require Northwestern to not only check you out, but ALSO to EXPLAIN how it is they arrived at whatever diagnosis they come up with, so you won't be left hanging the way you were.