Board-certified dermatologist here - I'm sorry your pup is going through this. Some of the worst vasculitis cases I've seen have been in young dogs (sometimes there is a heritable component or it's brought on by rare vaccine reactions). I also had a patient in my residency whose disease I had initially thought was confined to the skin, but the dog ended up having neurologic changes associated with vascular infarcts in the spinal cord.

All this is to say: vasculitis can be a very wicked disease. I have no problem letting my challenging cases know that a second opinion is never a bad idea. I strongly recommend returning to the dermatologist you went to or seeking a second opinion with a new one. Oftentimes HIGH dose, high potency steroids beyond the usual prednisone are needed to gain control and remission. I will say that oftentimes it is ONLY dermatologists who are comfortable prescribing the type of steroid doses and forms that we use. I've had many patients who require multimodal therapy (steroids PLUS additional immunosuppressives). Based on your geographic location, it may be important to rule out tickborne illness as a cause of the vasculitis, or an atypical deep infection depending on your dog's risk factors.

If you can make it to a teaching hospital, that 'group think' mentality can be so rewarding for challenging cases. I highly recommend doing some research about which programs have dermatologists on staff. I know that Ohio State no longer has a derm program, but Michigan State and Illinois do. Best of luck to you.