I had tenosynovitis in my left wrist a few years ago. It appeared really suddenly, one day there was nothing then two days later I couldn't bend my wrist or even hold an empty cup. I think it was caused by braking from brake hood just too may times; I was riding for about 6 hours a day five days a week in traffic.
As long as you kept the wrist straight there wasn't any pain. The hospital gave me a support to wear. It was a sort of bendy sheet plastic which is wrapped around the wrist and then sets rigid.
They suggested a cortisone injection; I said no. I had a few sessions of ultrasound but I'm not sure if it had much effect. It did get better, slowly. After about 6 months the pain was gone, but there was still lump on my wrist. Even now, that area on my left wrist is still a bit bigger than on my right wrist.