I know that in the US it is very popular to use hippotherapy for people with MS - it is said to be extremely helpful with weakness. I know that there is a lot of MS in Scotland (Scotland is known for having an unusually large number of people with this problem), and I am wondering if hippotherapy is popular there as well - you might find someone who is used to coaching riders who have weakness and/or other nerve problems.
The RDA does hippotherapy in which horses can be used for anything from a calming influence on a child with severe learning difficulties, to a physiotherapist for those with muscle/skeletal problems. Horses are also used for depression and Drug Rehab. So Hippotherapy covers a very very broad spectrum.