The condition was magically and quickly reversed at the very end of IM3. It must hold the record for the fastest developed cure in the history of the world. There's also the part where Tony actually could have removed the shrapnel at any time. Go figure.

I share some of these annoyances, but what I didn't understand is how Darren Cross could have been affected by the particles when he had not perfected the shrinking mechanism until the end of the film — and hadn't used the suit when Hope attributes the violent insanity to the particles.