Neither of my kids have any lung damage yet - based on their x-rays, CT scans, lack of culturing bugs, and normal PFT's. They both have some narrowing of the small airways but I have asked and just like bonniebaby says it probably a result of asthma or perhaps mucus, but the doctors don't refer to this as damage. I specifically asked if my daughter had any damage after her one bout with PA and I was told no. The doctor said he even had to argue with the radiologist as to whether or not she should have the dx of CF because her CT looked so normal.
So I think it is possible - just not very common, and as stated above "yet" may be the key word here. We count ourselves among the lucky and they both are very compliant with all their treatments..... so far so good