Hi, welcome to LWA :-)
The general rule for Multiple Sclerosis is that it causes obvious localised lesions seen on the brain scan, supported by Lumbar Puncture tests which show immune reaction to myelin etc.
So, what you describe doesn't sound quite like MS, but maybe more like the Doctors have called it "MS" because they don't actually know what it is. As others have said, I've also been told I've got "MS", or am just "assumed to have MS", without ever getting any tests, not even a brainscan. If it isn't MS, then I don't think most Doctors would know what it was, as most aren't trained in Neurology beyond the bare basics. When actual Neurologists examine me, they disagree its MS, but don't know what it could possibly be. In fact, it's likely to be either metabolic or an SCA, with an outside chance of an autoimmune condition or cerebellar hernia with neck problems etc.
For that reason, if the new Doctor is suggesting tests for other conditions to pin down what it might actually be, maybe "go with the flow" and see where it leads. You haven't got a lot to lose have you? And just maybe they'll be able to put a definite name on it.
Meanwhile, generalised inflammation of the brain with seizures occurs in a number of conditions. Without knowing more about your symptoms and history it's difficult to say which one or type to get tested for. For instance:
Have you had eyesight problems, and if so, are they more like Optic Neuritis (MS), Retinitis Pigmentosa (NARP, SCA), or a slow loss of eyesight due to eye nerve atrophy (SCA, LHON, many others)?
If the inflammation and damage is localised to one half of the brain, it could be Rasmussen's Encephalitis.
If it's whole brain inflammation, and came on in late childhood or teenage, then conditions like SSPE (inability to suppress the Measles virus) or others are possible. Adult-onset conditions include SPNE and Leigh Disease (SNEM, or else one of the 26 conditions under "Leigh Syndrome").
It there is evidence of missing white brain matter, a Leukoencephalopathy (such as Leigh Syndrome related ones, or MELAS).
If eyes, pancreas, kidneys, skin or other parts of the body are also involved, then maybe it's a systemic autoimmune condition like Lupus (SLE) or possibly Sjogren's Syndrome.
Ultimately though, it's often "much of a muchness" which actual condition any of us have got, as so many conditions overlap in symptoms and treatments, so the rest often still comes down to emotional support and practical steps to cope with whatever disabilities one might be stuck with.....
As Patsy said, at the end of the day, the purpose of an accurate diagnosis is to get the treatments which have proven to work best for that condition, and where possible, a cure, or at least something to stop it progressing. Since in most cases of inflammatory conditions, it's going to be Steroids with or without antibiotics/anti-virals, and then treatments to control and relieve specific symptoms. For metabolic problems, there's diet and supplements. So, I agree - if you're getting worse despite any treatment you're currently getting - try the new Doc with new ideas. You might yet get lucky :-)