I often find it difficult to respond to the greeting, "Hi! How are you?" Most people don't really want to know how I feel, so I usually respond with "OK" or "Working on it" or "I'm here." I want to indicate that things are not wonderful, but not to entangle them in a long, sad story.
When my friends (who really want to know) ask the same question, then I try to get a feel for how much they want to know, before I answer. I have one friend, who suffers from MS herself, who asked me "How can I best ask you 'how you are'?" I thought this was an excellent question - and I highly recommend it for friends of people in pain. My response was "Please ask what my pain-scale number is today." (Later in April, P=Pain Scale, but it's basically a 0-10, with 0 for no pain and 10 for the worst pain you can imagine.) So, whenever she greeted me, she asked my number. It was a great way for me to quickly let her know how I was feeling that day (I generally lived around 7-8), and she could rejoice for a 6 or give extra sympathy for a 9. It was an easy answer to give, and if I didn't want to discuss further, then I could quickly change the subject.
Don't be afraid to hear the answer to "how are you?" People in pain sometimes really just need to tell someone how much it hurts. Or share the good news of a better day. Or relate the frustrations of ups and downs. People who don't have chronic pain have the same needs. The next time you ask someone "how are you?" - stick around for the answer. You just might be the ear that they need!
What I've learned: don't be afraid to answer "how are you?" with how I really am.