What Causes Blisters On Legs After Botox Treatment For Leg Spasms?

Hello, I have an incomplete spinal cord injury of 6 years. Approximately 3 months ago I had a second session of Botox injections in my left leg for spasm. The first time had no impact so the dose was doubled for the second session. For the past 4 weeks I have had a series of one at a time large blisters on my right leg. The blisters morph into open lesions that take weeks to heal and have a dark coloration. My G.P. has me on a sulfamethoxazoe for a second time when the third blister appeared about the size of a quarter. This seems rather distant from the time I had Botox but it is listed as having side effects as blisters at sites distant from injection site. Are you aware of any connection of sores on the legs beginning as blisters several months following a large amount of Botox injected into the leg?