There are rules on Madness in RMSS Gamemaster Law, that treat it like a physical disease.
There are different rules on Madness in the RMSS Mentalism Companion also.
RM2's Rolemaster Companion 3 had rules for madness as damage (kind of) via depression, shock and stress criticals.
The Depression Critical is also part of the Shadow World Master Atlas appendix download:
http://www.ironcrown.com/ICEforums/index.php?action=tpmod;dl=item224
