That's really very sad to hear!
There is no evidence in the abundant literature on SCLS that back problems are a cause or a consequence of this illness.
I'm no doctor, but if you are losing the use of one of your legs, it sounds like one of your nerves is being pinched and you need to be operated urgently -- before the damage is irreversible.
If you cannot find a neurologist or back doctor in your area that will read the latest (vintage 2010) articles on SCLS featured in the Disorder Resources section of this website, which explain what the illness is and is not, then your alternative is to spend money on yourself and be seen and operated at a top medical center like Hospital for Special Surgery in New York (ranked #1 nationwide for orthopedics), or the Mayo Clinic in Rochester, MN (ranked #2), where they're not afraid to treat a patient with SCLS -- because they've done it before.
(I say that you'll have to spend money because they may charge you more than Medicare or your insurance will reimburse, and you will have expenses related to travel and room and board.)