Do a Google search for Kelly who used to post here - I think her
username is Snittens.  IIRC she has a cat with this condition.  Email
her - she's very nice and knowledgable.
-L.

There are two types of shunts- inside the liver (intrahepatic) and outside
the liver (extrahepatic). Extrahepatic shunts are much easier to repair.
Since your cat is so young, she probably has a congenital shunt which are
usually single, extrahepatic shunts.

Her stumbling might be caused by toxins in the blood from protein catabolism
going directly into the circulation without being detoxified by the liver.
A PSS causes blood containing toxins absorbed from the intestines to by-pass
the liver.  Until she has the surgery to repair the shunt, you might want to
speak to your vet about a low-protein diet (e.g., k/d) which should lessen
her symptoms. The lower protein content will produce less toxins.  You
should also speak to your vet about lactulose- its a laxative but it also
traps ammonia in the colon where it can be eliminated in the feces instead
of returning to the circulation. Ammonia is the chief toxin that's
associated with neurological signs in cats with PSS.

Most cats with congenital extrahepatic PSS recover completely, so keep the
faith!

Best of luck,

Phil