Good answer, Shell.
Remember that an MRI can only see lesions pretty much larger than 1mm. Well, within that area (1-2mm) are thousands of nerve axons (in the white matter) each with thousands of nerve connections. A few more involved and demyelinated nerves can be operating and the MRI will see no change. That is one of the great fallacies that the MRI will show a change when the symptoms change.
There is NO length of time when an unchanged MRI means that the diagnosis is not MS. Reread that last sentence. This is especially true is one is on a disease modifying med, but remains true untreated.
Q
HI Saggiom,
Welcome to the forum. It absolutely can happen from old lesions. It can also happen with new ones, and all inbetween. Not all lesions show on MRIs depending on the strength of the machine, but what is more important to know is that not all lesions equate to MS symptoms. So, I'm sure that provides you no comfort, but it really can be either scenario.
You mention "more" pain in your arm, and tingling. Is this pain/tingling something that has been typical for you throughout your time with MS? If so, and you are experiencing an increase w/out a decrease, it's worth mentioning to your neuro. For some people with MS this could indicate an exacerbation, for others, just chronic ongoing symptoms and no attack. Your history is your biggest indicator. And, the other scenario is a pseudo exacerbation. This as you may know can be brought on by heat, stress, etc. However, the symptom should decrease once the trigger is removed.
It's a good rule to jot it down, keep an eye it, and if it subsides write that down too - especially if your regularly scheduled neuro exam is a ways off. It's easy to forget things that happen on and off.
Hope this helps..
-Shell