K.N.
if your son does have psoriasis of the nails, there probably isn't much the dermatologist can do for him. i was diagnosed with it at age 11 and still have it. the good news is that it really hasn't had much of an impact on my life (aside from being self-conscious as a pre-teen). it's unsightly, but most people don't notice anyway.
sometimes my nails do get a bit thick or spooned, and when this happens, they get sore, but a podiatrist or nail tech can smooth them down, which makes them feel and look better.
you will want to see the doctor to rule out fungus and who knows, maybe there are some new treatments that can clear it up. i haven't seen the derm about it in fifteen years. you will also want to watch his skin to make sure it doesn't develop there. i'm sort of an anomoly, not having it on my skin, but i do get patches occasionally when i'm really stressed out. it's usually easy for me to clear them up, but they're so uncomfortable. there are a few books out there about diet and psoriasis that you might want to look at, also.
but really, i can't stress enough how minor a problem this has been for me. try not to worry too much about it.
best of luck to you both.