I'm not sure what you mean by "if demyelination does not progress."
Demyelination is a has a very broad meaning and is used as a term in many diseases not just Multiple Sclerosis.
Multiple Sclerosis is a disease of the Central Nervous System(CNS) which includes the brain, spinal cord and optic nerves. Lesions can show up in any or all of those areas. Multiple Sclerosis does not cause problems with the vertebra or discs. Low back pain is usually due to mechanical back problems. Multiple Sclerosis does not cause joint damage.
Please do not discount your diagnosed back problem. My husband had his 2nd lumbar surgery this past July. The first surgery in 2008 was done due to a bulging disc. He had low back pain, sciatica, difficulty walking, numbness and tingling in feet. This year he had no back pain but his symptoms were foot drop, pain in his leg, leg giving out and almost lost his ability to walk.
Even if surgery is not recommended for you Physical Therapy(PT) can help decrease symptoms of mechanical back problems.
Diagnosed with Multiple Sclerosis in 1985