I'm so sorry your feeling let down, and rightly so as you have so much information in the letter and by the sounds of it not discussed at the appointment. Were you showed the letter during the conversation with your specialist?
I feel your frustration and I'm glad you have the appt with your GP on the 5th. As you said discuss it all at that appointment and see what they have to say. Another thing is that, if your really not satisfied witht he Rheumy you saw maybe ask to be referred to another one, sometimes it takes people a little while to find the right one. May I suggest you right down all the things you want to ask and discuss in a note book and take it along with you, so you don't forget something. Also I have found that having someone with me to write down the replies is sometimes a help as your so involved in what their saying you forget somethings. Just a thought and that way you will come out with your answers and hopefully a plan of what's going to happen next.
Don't let them get you in and out feeling rushed, be firm but not aggressive, this is your body and your pain.
This site is wonderful for getting feed back on questions, usually lots of people with views from all angles. Don't let this get you down, do some research on the internet with regards conditions confirmed in your letter and that way you will be more able to discuss them and how you go about resolving them.
Most of all, keep us informed, vent your frustration here and ask anything you want.
Take care and good luck on the 5th, thinking of you.