Hi all, i'm wondering if this might be box blight, although i have a suspicion it may be the cat from next door that has caused it, either way, is it likely to re-grow if it is just kitty wee wee? the rest of the hedge is fine.
I'm no expert on this Pat - but if it's just that one area, it may well be cats marking territory. If you can block it off for a few days you may see an improvement as it often deters them from using that area. It can be very destructive - not to mention annoying when it happens.
If nothing else, my post will send your query to the top of the page for a while where someone else will offer more advice
I think the smell of box makes it a target for cats - mine gets sprayed too. It seems a likely possiblity, as the dead growth doesn't extend all the way up the stems except in the centre of the area.