Looks like Pseudomonas syringae, a bacterial blight. Sango Kaku and other red barked JM's seem to be overly prone to this affliction (although other cultivars are affected as well).

This pathogen affects scores of different plants, some only cosmetically and others somewhat more severely. With maples, the disease seems to be present in spring after a tough winter. Stem and branch tips that have been hit by cold are then infected with the pathogen during damp springs as the trees comes out of dormancy. Often the disease can be halted or at its least progress checked by pruning out the infected wood. The presence of the disease and its location is indicated by the blackened portions on the stems.

You could conceivably save your tree by pruning out all the bare top branching down to where the trunk retains its red coloring. The two leafed out small branches on either side of this area are also showing symptoms of psuedomonas and probably should be removed as well.