Thumb and wrist pain in left hand when wrist is bent forward (hand towards me). Pain located on the thumb side of the wrist only. What could this be?

DeQuervain's. This is tenosynovitis of the first dorsal compartment of the wrist. You have basically performed a finkelstein test. Go see your orthopaedic surgeon for evaluation and treatment.
De Quervain's? It's hard to tell from your description, but de quervain's tenosynovitis is a possibility. Any sort of muscle or joint pain, or irritation of the tendons or ligaments in the wrist, and other more serious problems can cause similar symptoms. Rest, ice and elevation can help, but persistent pain should be promptly evaluated by a qualified hand surgeon.

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Wrist pain Left only, on thumb side of wrist and down a little toward thumb. Can't lift/lean on it ~5 days. Appt next week. What to do til appt?

Wrist splint and ice. You can always go into an urgent care to get X-rays immediately. To wait until your appointment, you could buy a wrist splint that also immobilizes your thumb to help relieve pain. Icing the painful area for 10-15 minutes a few times a day can also help. If not allergic, you can take Ibuprofen 600mg every 8 hours and also Tylenol (acetaminophen) 500mg every 6 hours as well to help reduce pain. Read more...