PsA is Psoriatic Arthritis. There are more than 1 type of that. RA is Rheumatoid Arthritis, AS is Ankylosing Spondylitis. These can all be learned about better on the following websites: National Institute of Health.org; Mayo.com; Medical News Today. Com. You can also do a simple Google search of your questions for more info. That's how I started a few years ago. You need a Rheumatologist to diagnose you. If you don't already have one, most, but not all, require a referral from your regular family dr. I hope this helps.