Defeasible reasoning in medicine

I am looking for modern platforms that support automated defeasible reasoning and decision support for a medical application. My graduate work (back in the mid-90s) helped build an agent-based defeasible reasoner and implemented a primitive "Medical Diagnostic Advisor". I'm now working with a company that needs a *defeasible* rule-based engine to support decisionmaking in real time based on input from a monitoring system. I was hoping someone could point me in the right direction for the latest developments in defeasible reasoners, preferably LISP based, although C/++/objective is fine too. Thanks!