Did you ever determine what happened to the leaves when the shrub leafed out in Spring? Knowing that, you could take corrective or preventative action but, I am not sure we can guess what happened or what can be done very well..

My first choice: Be on the lookout for deer, who like to eat the flower buds and who
may also nibbled on your shrub's leaves and stems when one is not looking. They LOVE hydrangeas. :o)

If the leaves dried out, explore watering issues (make sure you use about 1 gallon of water per watering in Spring; 1.5 gallons in summer). Add mulch to protect the roots and make the soil moisture last longer.

Did I already say this: be on the lookout for deer. They LOVE hydrangeas. :o)

I looked at my PeeWee this afternoon and it is getting big enough where, if my PW were to loose leaves, the leaves on higher areas will hide this issue. I suspect yours will eventually do the same if this reoccurs.

Some hydrangeas are also notorious for showing their feet (Limelight sometimes does this). But oakleaf hydrangeas typically don't unless something causes this problem.

In the meantime, consider adding companion plants that will hide this (annuals perhaps?). The shrub may decide to develop new leaves this growing season but that is up to the shrub to do when it wants to do it.

thank you...no deer around here. I have three of them, one is doing great, the other (planted in same area) have leaves on stem but very tiny and not getting any bigger. The very top leaves are normal size. This is their first spring, so maybe just need to be established. Should I prune after flowering, would this help the problem?

I would just let them continue getting TLC (even moisture, fertilizer, mulch) and see if they improve next year. Pruning of a stem will just produce side branches below where you cut and maybe do nothing to the lack of leaves at the bottom. And worse, you could end with a single stem that has many branches and many heavy flowers that could cause flopping of the branch when wet if the plant produces a lot of flowers there.

A high nitrogen fertilizer in early Spring or use of alfalfa might help but probably cannot be directed to cause leaf out exactly where you want it... But it would be nice if we could do that?!?!!! If you want to use fertilizers now, do it before the end of June or so (nitrogen keeps the plant in grow mode but you need it to go dormant in Fall).