Canine Rage Syndrome

Question
I took in two foster dogs, littermates, and the one has shown signs of unpredictable aggression.  He is 3 years old and his littermate does not have this behavior.  Knowing he was severely abused by  his backyard breeder (tethered to an 8 foot chain in a basement his entire life), I worked with him for two months and he was much improved.  He is also on Zanax (low dose twice daily).  He was adopted to a woman who stated she had experience in abused dogs, this breed (Keeshonden), etc.  She lives with her elderly mother, no children, no pets.  Now after 3 months, she took him off the Zanax cold turkey for no reason and his behavior has not only returned, but has escalated.  It won't be long before she returns this dog to me.  My question:  Is there any reason to hope for significant improvement that would allow this dog to either be adopted out again or remain in my home without fear of severe aggression?  I run a rescue and pet sitting business out of my home so there are always other dogs whose well being is my responsibility.  I am not comfortable evaluating this condition myself, although I've retrained aggressive dogs in the past, but not at this level.  I do not want to euthanize him if there is a chance he can be helped.  He is a purebred Keeshond and otherwise healthy, but his behavior is now unpredictable and frightening.  I instructed the new owner to put him back on the Zanax immediately and not to change his dose for any reason without an expert veterinary opinion.  This dog now lives four hours from me so I cannot observe his current behavior, but it sounds like it has escalated from when I first got him.  Any advice would be appreciated.

Answer
I have terrific respect, admiration and affection for those who are doing REAL rescue work, such as yourself.  I know that your home is full of dogs requiring rehabilitation and responsible placement, and I know that filling a permanent place (such as you would have to do with this dog) means one (at a time) dog that will not receive your expertise and care.  However, in the case of this dog, it should be immediately removed from its adoptive home.  And then, after replacement of medication, carefully observed and worked with over the course of not less than 18 months.

The fact that the dog's "rage syndrome" (which is actually a demonstration of low level temporal lobe seizures, if it is indeed rage syndrome) responded to Xanax means one of two things: it is neurological, or it is fear related.  If it is neurological, medication to control seizures should (SHOULD) help; if it is behavioral, you will see the difference in the dog's foundation behavior within 48 hours of getting him back, and you will be able to determine from there whether or not to place him again.  PLEASE REPOST as often as you need to with ANY questions, observations and regarding any plan to modify behavior, following your close observation after reclaiming this dog.  DO NOT HESITATE TO GO TO GET HIM, this is an absolute necessity.  BTW, I have seen several Keeshonden for various aggression problems, every single one of them fear related.  WHEN you repost, please be specific in your subject line, a/k/a: repost Keeshond rescue.  Thank you.