Typical a injection of prednisone is given in the effected area by the to help reduce the inflammation and provide some help with the pain, prednisone tablets may be sent home with the client to give orally afterward. This is usually the first stage of treatment here and then a waiting period to see how much recovery the dog will gain, MRI like you mentioned would be the next step, sometimes a dopt would be referred to a rehab center which would use treatments such as chiropractor. acupuncture, ultrasound treats and physio therapy exercises to regain back function, in some case surgery is needed in which they fuse the spine and often that is also followed rehab.
This link you may find helpful
http://www.marvistavet.com/html/body...ed_animal.html