。
I'm wondering if I might have tenosynovitis.
Literal
Tenosynovitis is-not [quotative-かと] think [explanatory-のです].
A patient's tentative self-diagnosis. 腱鞘炎 (けんしょうえん) 'tenosynovitis' (tendon sheath inflammation) is a specific medical term — the repetitive-strain injury common in musicians, typists, and assembly-line workers. ~ではないかと思う ('I wonder if not X' = 'I think it might be X') is the tentative/worried hypothesis form. のです is the explanatory ending, softening the claim.