Ok, so I went on a 10 day climbing trip (a lot of bouldering involved) and got back about a week ago. I hadn't noticed anything hurting (and I've never had any climbing related injuries), and then my hand seemed to spontaneously start hurting. I'll try to describe where it hurts the best I can: if you open your hand and draw a line from your pointer finger down towards your wrist, and then draw a line from your thumb down towards your wrist, the pain is coming from the intersection of the two lines. It hurts when I'm doing a pinch, or more specifically when I'm unlocking my front door (so pinching and twisting). Like I said, I don't remember any specific move I did for it to start hurting like this, so if it is climbing related I'm guessing it's more of an overuse thing. Any ideas what I've done?

I had something similar happen while bouldering about 9 months ago. It felt to me like a strained tendon. I layed off it for about two weeks, then did light bouldering with no pinching and worked back from there... hope that helps :)

I have something that sounds similar, but less intense and very persistent. It goes from ache to pain at worst and is in the area you describe. The first time it occurred was after crimping and cranking on hand jams and it lasted about a year until ibuprophen and a LOT of icing knocked it back. The other day I was falling off a sloper repeatedly, and it seems to have returned. Get the Cryo-cuff out of the closet! It wasn't really pinching that started it, but pinching seems to be the thing that bothers it. Let me know if you find anything, and I'll do the same. Good luck!

If it's in the meaty part of your palm at the base of your thumb, it could be muscle strain. Just thinkin'...

A-
My two best guesses, w/ out actually getting to see your hand, would be that you did indeed overuse it in the course of your 10 day trip. It sounds like you may have irritated the 1st metacarpophalangeal joint/ the joint at the base of your thumb. Pinching and crimping in some positions can put a lot of compressive and shear forces on this joint, so if you were projecting something w/ a weird hold that required a lot of thumb strength you may have pissed it off that way.

The other possibility that also comes to mind is that somewhere in the course of your bouldering you tossed for a sloper and smacked the base of your thumb bruising the part of the scaphoid or trapezium bones. This is pretty easy to do and the resulting periosteal irritation can definitely make pinching (especially thin holds or objects like keys) painful.

Treatment for either case is pretty much the same. Rest. Icing will help, I would stay away from the NSAID's, but mostly using the hand lightly so that whatever you're doing doesn't cause it pain. If you can climb on holds that don't cause it to be irritated or painful, the climbing shouldn't set you back in the healing process.

But as always, it's your hand and therefore ultimately your decision. If the pain has been persistent since you noticed it and or has gotten worse I would certainly recommend having a doc take a look at it.
Hope that it's minor and you're back at it soon,
BA