I did put one of my dogs through surgery for SM - I took him down to Clare Rusbridge at Stone Lion in London.
Clare Rusbridge gave this information:
Cranial/cervical decompression surgery is successful in reducing pain and improving neurological deficits in approximately 80% of cases and approximately 45% of cases may still have a satisfactory quality of life 2 years postoperatively. However surgery may not adequately address the factors leading to SM and this appears persistent in many cases. The clinical improvement is probably attributable to improvement in CSF flow through the foramen magnum. In some cases scaring and fibrous tissue adhesions over the foramen magnum seem to result in re-obstruction and 25% to as many as 50% of cases can eventually deteriorate. This can be as early as 2 months postoperatively.
My experience is that the disease will progress in a 1/3 of cases and this manifests as increased pain (e.g. frequent vocalisations and other behaviour suggesting discomfort). There may be ataxia and paresis however it would be unusual to progress to paralysis.
My bold highlights - we have to remember the short lifespan of our dogs, the average life of a Cavalier is only 9-10 years, so even the one month confinement following surgery is quite a long period of time for them.
It is very hard to make a decision as there seem to be mixed results, we hear of a lot of cases not doing well post op, but not sure if these are reported back to the surgeon as sometimes they are producing figures quoting very high rates of success, especially in the US. There seems to be little in the way of organised studies to demonstrate the effectiveness of surgery, but I don't think this will change as it is impossible to know whether the dog would have deteriorated anyway - this is a progressive disease but it progresses at different rates in different dogs, and sometimes they seem to remain the same for many years.
My own dog was very severely affected, he had the worst scan we had ever seen [the cerebellum was prolapsed right through the foramen magnum, but you would not have known it as he showed very little in the way of symptoms] we were told that surgery was really the only option for treatment for him. He had an amazing recovery from surgery, he remained on some medication but sadly within 6 months the symptoms returned. He deteriorated fairly rapidly and was euthanised 10 months post op to prevent further suffering.
It is quite traumatic both for the dog and the guardians, you will read many stories on here, sometimes things don't go too well and they have a difficult recovery.
I feel we gave him the best possible chance BUT I don't think I would opt for surgery again. This is just my personal opinion and also takes into account our personal situation - the very long journey involved, the time away from home, and the effect on everyone. [I'm full time carer for my husband in addition to having multiple health issues myself] This was only made possibly by the kindness of friends, in particular Margaret Carter on the board, who not only accommodated us but also took us to and from Clare's practice. [and put up with Rupert, who had to travel with me and caused chaos wherever he went, fortunately he was really well at the time although it was actually only about 7-8 weeks before his last illness
. We took him to a large pet store and he was either up the shelves trying to get to the goodies or diving underneath them to pick up things that had been dropped there! Wonderful to see a 12 year old enjoying himself so much!]
The other dogs have all been treated medically, also with homoeopathy and now McTimoney chiropractic treatment too [under the guidance of my neurologist]. We have had mixed results - sadly the cocktail and high doses of drugs Teddy had to take to keep him comfortable, apparently caused heart and liver issues
I think when we have been through years of treating our dogs we tend to forget that actually these drugs are very powerful and not everyday veterinary medicines.
We were fortunate that our insurance covered 90% of the cost of the surgery but obviously not the travel, accommodation, meals etc So there is a financial consideration too. We all want to do the very best for our dogs but you have to think it through very carefully - probably best to do this at the time of first diagnosis.
You make a decision at the time based on the information you have before you, discussions with your neurologist/neurosurgeon and vet, hopefully also with your family and friends. You can torment yourself over whether it was the right thing to do, but you cannot change the past, you did your best out of love for you dog.