Spinal Epidural Lipomatosis (rare)
 

An accumulation of fatty tissue compressing the spinal nerve, most common cause said to be long term use of steroids though also associated with obesity. Neither cause applies to me unless a single cortisone injection given many moons before the symptoms of neuropathic pain and neurological deficit affecting my mobility became apparent, so I guess that the 'autoimmune' catch-all term applies.

Any experience of similar condition would be most welcome.