I don't think there has been really new developments lately, but
I myself have recently found Chinese herbal medicine, seems to work better on my spastic muscles than Baclofen for example. Obviously Chinese medicine is very old, just new to me
Have tried diazapam too, but that didn't really work for me.
Stemcells could be used on adults as well as in children, I think China has the most experience in that, anf that is newest treatment I think.
Selective Dorsal Rhizotomy has been around for years, and works on adults as well as in children, not many people know that.