So sorry to hear about this horse, It doesn't sound like a very nice disease :( I read the following on thehorse.com :
There is no effective treatment for shivers. A horse might improve with rest, but shivering will return when exercise resumes. Some owners feed a high-fat, low-carbohydrate diet similar to that used to manage PSSM, and this might help early in the disease. In another study, clinical signs did not resolve when fed a high-fat diet.
Some days are better than others for some shivers-affected horses. In general, this is considered a progressive, debilitating disease with a poor prognosis. Clinical signs eventually increase in frequency and severity, and muscle wasting and weakness worsen. The course of the disease can progress rapidly or take as long as 24 years to render a horse incapacitated.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France