Acer palmatum 'Shania' problem

I think my Acer palmatum 'Shania' is starting to die back as clusters of leaves are becoming shrivelled and dry. It has been planted for about 3 years and has seemed happy in its position until now. I have read of similar problems on ubc botanicals forum with suggestions that it might be infected with Pseudomonas or that Shania is more fragile because Shaina is a witches'-broom and brooms are weak and unpredictable:
www.ubcbotanicalgarden.org/forums/showthread.php?t=26326
Has anyone else had similar problems?
Nicand