Japanese Maple is dying
Here are some reasons for decline/branch dieback on your Japanese maple. They are subject to many environmental stressors such as drought, poor drainage, too much moisture, temperature extremes, too much mulch, planting too deeply, soil compaction, etc. The root system is growing in a limited area next to concrete. Look at the attached publication for more information on these types of problems. http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG86%20Common%20Abio...
Also, during cold winters and temperature fluctuations sometimes the bark can freeze and kill the cambium which can cause dieback. If the tree is grafted sometimes the graft will die. If your maple is located in a southern exposure or a windy spot, it can suffer extremes from wind and cold. These trees grow best in a drained soil in morning sun and afternoon shade protected from winter winds.
Scratch the branches with your fingernail and look for green tissue. If you see it, the branches may still be viable. Otherwise, they are dead.
If viable, prune dead wood, make sure mulch is no thicker than several inches and keep away from the base of the trunk. The tree will most likely limp along and you will have to consider replacement in the future. You may want to select another type of plant for the site as it is growing next and over the fence.