Dear Doris -- I hope that the reason you ask for this information is not too close to home. I don't know anything about it myself, but the following reference may be of help. The journal should be available to read or photocopy at any University library which teaches Veterinary Medicine or Veterinary Science, or you can order it through the free medline search service (only the searching is free!) for about $25. This is the URL for the free medline:
and this is the only relevant reference that I could find:
Vanvooren N; A suspected case of idiopathic generalised tremor (shaker disease) in a shih tzu. (Veterinary Record. 136(22):568, 1995 Jun 3.) Unique Identifier 95407046 Good luck!
Deanna (Moose & Squirrel) 12-10-97