Maple Tree Leaves Dying in Patches?

I have a maple that is approximately 20 to 25 years old. About three years ago, it began losing large areas of leaves by late June. The leaves turn, but the rest of the tree has what appear to be healthy leaves. The following year, the leaves do not reappear leaving large areas of the tree bare. At this point, probably two-thirds of the tree has no leaves.

I'm concerned at this point that I'm going to lose this tree.

Any suggestions?

By Wilf B from Lunenburg, Nova Scotia