Lynn, my dog Friday has severe SM. She showed signs before 1 year of age, but I've never seen her limp on her front or back legs. I've talked to people who experienced weakness in their rear legs, but not on the front. I'm by no means an authority on SM and there are others here who are a better authority than I am but I don't know if I would jump into having an MRI done that soon. We did have one on Friday but only after everything else was ruled out. It's an expensive test and because you have to put the dog under general anesthesia I would consider it invasive and not taken lightly. I don't want to discourage you and tell you not to take your vets advice but I would do some research on your own first.
Any symptoms that Friday showed was continuous and didn't go away. Does she scratch? Is she sensitive on her paws or chest or ears to touch? Friday showed these symptoms probably by age 7 months, but no limping. I just hope everything turns out ok!!
Terri, mom to Monday, Wednesday, Friday and Sunday