I've quite a few hydrangeas - and some in the more exposed areas are like yours, EJ....I've put it down to the frost and hail we've had at unexpected times, given that the extreme weather was sandwiched between mild stuff. Poor things were woken up by the sun, bashed on the head by the hailstones, woken up...got to get out and cut mine down, too.....BUT...see that there's lots of new growth from the base emerging. I've been seeing exactlythe same pattern in other gardens, too.
Hope this reassures you a bit?
Cheers! Lish