It may have been attacked by a fungal infection. Cut off a small branch and see if there is any brown ring around the inside as this often indicates a disease.

Probably verticillium wilt. Catalpa is prone, as are some acers. As above, cut off a small branch and look for tell-tale brown ring. Cut off and burn infected branches, water tree well and feed, but not with a high nitrogen food. No cure as such. If tree succumbs, replant with a disease resistant genus, rosaceae usually pretty strong. There are lists available (e-mail me if you need)
PJ