There are several bacterial or fungal diseases that hydrangeas can suffer from.  Just judging from the photographs, your hydrangea appears to be healthy other than possible fungal issues on some of the leaves probably caused by excessive moisture.  From what I am able to see, the stems look healthy.  It may have been grown in a container and watered overhead when humidity was high.  I just don't know all of the circumstances.  There are fungal sprays that can be applied.  If you have recently received this plant and all of the leaves have suddenly wilted and fallen off, I would contact the nursery where you purchased it and talk to them about it.  I would also send them the photographs so they can see what is happening.

Hope this helps you.