Ms cannot be diagnosed until 2 specific " attachs" have occurred. They can be months or years apart. Sometimes people will have transverse myelitis then not have a second episode for years. You can indeed have MS with a clear MRI, but it is unusual. If that occurred, time and patience is needed to just wait and see whether the condition is MS. I personally had 2 sets of MRI during the diagnostic process, 2 years apart, which were both clear. I did not have sensory issues apart from a predisposition to pressure palsies. I was a bit disappointed that I did not have ms because disease modifying agents are available and the efficacy of the treatments are improving all the time.
I still doubt that I have PLS, but again time will tell. You certainly need a great deal of patience, when a player in this game!
Ask any questions you want. Hope this helps a bit. My husband is a neurologist and I did ask him on your behalf.