There's an interesting article on how to communicate on health forums in the USA Weekend. I've quoted a few of the tips that I thought were accurate here, and there's a link to the whole article at the bottom:
Find a board that will help you. Every health-related category may have subcategories or highly specialized boards. You need to find the discussion board that deals with your situation specifically; a topic such as heart disease may have subtopics related to diagnosis, surgery, smoking and exercise. Also, make sure that the discussion board is active. Look for daily postings as you scroll down through the contents. If the last posting was a month ago, you may not get prompt answers.
Check your emotions. ... Making liberal, unnecessary use of fuming ALL CAPS letters and exclamation points may keep you from accomplishing your goals -- and alienate you from other users.
Sharing is good. Some people struggling with a disease may receive news that they're making a great recovery, yet they are reluctant to share this because it sounds like "gloating" in a forum used by fellow sufferers of the ailment. They shouldn't. The reason people flock to these chats is because they want to hear from those who are doing well -- and how they did it.
Similarly, some are reluctant to talk about their setbacks because they don't want to dole out bad news to the group or are afraid of being discouraging. Again, the whole point is to share. If you're alone and hurting, don't be afraid to seek out shoulders to lean on. Someone even may have something practical to offer, like a new remedy or just-released study.
Participate regularly. Make the bulletin board part of the recovery routine by checking in every day. You'll feel more empowered to take control over your own health care and less afraid to consult with your doctor about possible treatments. Which brings up ...
Check out everything with the doctor. Most people on the boards are well-meaning folks who want to help. But such users may offer advice that's not right for you. The forum is never a substitute for sound medical advice. An exercise that helped someone build bone strength may be too strenuous for you, and a new drug may not agree with other drugs you're taking.
Link to whole article.