I can't answer all your questions but I can add to your knowledge by sharing my experience. I am now in my early seventies. Nearly ten years ago my walking mobility suddenly deteriorated and neuropathic pain from the hips downwards correspondingly increased, having been relatively mild for about 15 years previously. Best descriptions I can come up with for the mobility problem are heavy legs and poor balance.

After investigations including MRI I was given a spinal decompression operation which did not alleviate either problem but, so I was told, would stabilise the condition which was stated to be, yes, myelomalacia. The surgeon avoided questions as to cause saying at one point: "you won't hear that word from my mouth", the word in question being 'injury'.

The condition has indeed been stabilised so at least in my case myelomalacia doesn't appear to be a progressive condition. Various medications have had no effect on the neuropathic pain, which is ever present. I have occasionally searched for more info but usually come up with no more than 'softening of the spinal cord'.