A therapy dog and a service dog are 2 different things. A therapy dog is trained to go and visit hospitals , nursing homes , and is certified to do so.
A service dog is trained to perform special tasks for the disabled individal . the animal can be any size ... Sometimes other species of animals have been used for a service animal.
The aniaml can be trained by a professional , or can be trained by it's owner. A DR. writes a letter stating that a service animal would be helpful to the diasbled person.
I have only seen serious cases of disabled individuals who have a service dog. However, their are all kinds of disabilities out there. Dogs are amazing service dogs.
I have 2 of them ....
it is a good idea to have the basic training down with your dog. That would be the first step .