Cut it right back to where the leaves are, give it a good feed and wait and see what happens. Seems a bit late in the year for frost damage, or have you only just looked at it after the winter?

This happened to my Pittosporum tenuifolium 'Irene Paterson' It looked very bare with all the leaves on the ground. I cut back all over but left the long branches so was able to keep the height. Although it sprouted new growth almost at once it took two springs to recover and look good again and this (3rd) spring its totally covered in leaves and looks better than ever with its little flowers. I also fed it with Vitax Q4 and did water it that year while it regrew.