My left index finger hurts on the middle knuckle. It started about 24 hours ago, out of nowhere. I was just sitting at my computer, and the knuckle hadn't been injured or overworked in any way. It doesn't hurt as long as I don't move it, but if I apply a slight amount of pressure it hurts tremendously. If I apply more pressure, it starts hurting less. Heat or a vibrating massager also temporarily stop the pain, but it resumes within a minute after I stop. I'm pretty sure I have rheumatoid arthritis genetically, and this is showing symptoms of that so far.

Could it be something more serious, and what can be done to treat it?