(PP)Multiple Sclerosis new lesion took out my guitar playing.

I have played guitar all of my life (I'm 58) and even with PPMS for 20 years I've been able to play by using ergonomic devices and playing light instruments. Then, first week of March I had a new, bad lesion and after months of physical therapy the only thing that has not made progress is my left hand. The pointer finger wants to claw up and lock, the others all want to freeze and I can't stretch between fingers. Is there a medical procedure that will help? Will botox injections help? I heard they weaken the muscles and my left hand is already too weak to open a soda can.