"My 62 year old brother is 5 years into a Parkinson’s Disease diagnosis. He is stable for now while being treated by a neurologist with PD medications. However, his herniated discs give his constant pain. After two years of steroid injections, their effectiveness seems to be waning. Would a salve, lotion, or patch help with his pain?"
A salve, lotion, or patch could help with his pain. Many find topicals effective for back pain as they interact the cannabinoid receptors in your skin that help to control pain and inflammation. When patients add THC, THC-A, and CBD preparations to the affected area, they find it reduces the swelling and pain response of the area, providing a good deal of relief.
Personally, I use topicals everyday for my back pain. I do not go through anything as serious as your husband, but my own disks are not so great and topicals really help me to mitigate my pain.