Cat Litter & Health Problems?

Has anyone here had any experience with their cat's litter causing the cat health problems? I have heard that the scoopable stuff, which I've used for years, can cause serious problems in many cats.

I'm asking because Puddi-Da-Tat has been having some health issues for the past few months and we have not been able to identify what is wrong with her. It started out as what we thought was "hair balls," but she has also had an ongoing cough and sneezing. The vet has examined her and taken x-rays of her lungs, but she would not cooperate with him. Meaning, she does not display any of her symptoms while at the vet's office and ... *sigh* ... his impression of her is that she is a very robust thirteen year old with an ever-so-slight weeze in her chest when he listens to her breathing.

Unfortunately, that's just not true. Something is definitely wrong with her - she is not herself. She still has the sneezing/coughing fits at least a few times each day. We agreed to start giving her an antihistamine 2x/day for the past week, but I'm not seeing any real improvement with her.

So, that leads me to my question. Do you have personal experience with problems associated with kitty litter, and if so, what happened and what were the symptoms?

Thank you in advance!