Tenosynovitis/ de Quervain’s disease: occurs when the tendons around the base of the thumb are irritated or constricted.

aaackkk..
my 'ergonomic' mouse (the likely culprit) is now in my left hand and at a new/better height...
looks like a good time to send my lens off for its warranty repair!
(and perfect my "Helena Bonham Carter" look)
shot left handed... not for the faint-of-heart