I've had the same problem, gave them some extra feed although it was to late to save the affected leaves. I have taken out the leaves and a few more to allow light into the fruits and the plants seem to be responding well. They have formed lots of cascades of little cherry and plum toms so I think the remedial action has worked. But I still don't know the cause. Although I did loose some plants to potato blight.

I think tomato plants do this as they mature. Just remove the shrivelled leaves and unless the problem carries on further up the plants I wouldn't worry as they look healthy.