Ken I had some in my garden (two houses away from this garden) that were cold-damaged and they have all recovered now so we sort of ruled that possibility out. The damaged Hydranea are not isolated at all, they are in the same flower bed about 10 or 12 feet long intermixed with healthy Hydrandeas between the two sick ones. If it is some sort of insect then it seems they all would have been nibbled on and I don't think she saw any signs of bugs.

Still a mystery.

Looks like the damage is starting at the leaf edges and working in. Usually a sign of not enough water. Maybe the roots were damaged or eaten.

Inconsistent watering and cold damage can cause this look. If the leaves now brown out from the edges inwards, the soil needs more water. use enough water to moisten the siil down to about 8” deep if you test several spots under the drip line. Aim to keep the top 4” or so evenly moist/damp always. If the problem was present at leaf out time, the cause was winter related. If the problem occured after all danger of frost had passed, it may be due to inconsistent watering that allowed the foliage to dry out. Note that some leaves appear chlorothic so check the soil pH and make sure that you are currently not overwatering.

I too believe it could be some sort of root damage. Voles? Partial root rot? (drainage is not always consistent all through a garden)

The foliage looks misshapen or distorted, as well as undersized and I've never seen that as a result of a water issue, OTOH, a partial root rot that started during the winter months might account for that.

Thanks everyone- all excellent advice and speculation on this issue.

I had not even considered what is going on below the ground with the roots.

I will pass along all of your input & information to my friend with the sick Hydrangeas.