Skimbleshanks
Sorry to hear you're having such a tough time with reaction to the methylprednisolone. I'm not familiar with this particular steroid and certainly have no medical qualifications to give you advice - but from a fellow patient's point of view if I had this kind of reaction I'd be asking questions of the doctors who administered the medication. If it's not easy to get to them then have your PCP follow it up (when you get a new one.) From what you wrote it sounds like they gave you the steroid before they had confirmed an MS diagnosis - did they explain why they did this? I'm sorry I can't comment on your MRI results - that's beyond my intelligence (what's left of it!)
Re steroid medication staying in the system - it varies - some are intended to be long lasting (those injected into joints last about 3 mths). I'm on 5 different steroids - one has a half-life (active time in the body) of about 6 hrs - three others are 24hrs and yet another is 48 hrs.
It sounds like you're beginning a journey to what might be a prolonged diagnosis and treatment. Hang in there. I understand how scary it can all be - after my last visit to the ER I'm dreading having to go back. One way I've found to keep on top of the fear is to take control of what happens to you as much as possible. This means getting copies of your hospital records, any test results, appointments etc. and setting up a filing system so that you can find what you need when you need it - for me confusion just makes me more anxious. Do what you're doing now - get info - you've probably already searched the MS forum on here. Prepare for appts. - write questions down. I keep a time-line record of new symptoms as they appear - it's then easy to just print it out and take it along to your diagnostic appts. Trying to remember back months or years while in an already stressful appt. is hard - much easier to just hand a sheet of paper to the doc. Line up your support system if you can in advance - ie: have friends or family that know what's going on and can be there if needed and can act as an advocate for you if the system is stone-walling you. Try and keep a sense of humor - if all else fails laughing at the system can make the wait bearable.
Just to clarify some of my comments - I'm in a different country to you and have to endure a Public Health System - years ago I lived in the U.S. for a while so I have some knowledge of the American system (although pre the new changes). So if some of what I say seems weird to you that's probably why - the systems are very different. For example you're waiting for a neurology appt. - same here - however my referral was made by my endocrinologist back in Dec 2014 - it wasn't assessed until Feb 2015 (fortunately they deemed me 'worthy' of their attention) and I've been told I may get an appt. in 4 mths. Patience required.
Sorry this is so long-winded. Hope it's of use. Happy just to listen if you need to vent your concerns.