Does your lawn look like this now? If so, it's not some super, secret disease, or a winter bug. No, this is called your dogs present to you after peeing on our precious lawn all winter. We love our kids but they can cause some damage other than the mud like burning your lawn.
Best thing to do here is take a shovel and poke it up and down on the edge, slicing through the thatch area. Then throw down some seed that matches your lawn and poke it some more with the shovel. Normally this will recover in about 3 weeks if you have moved the dog to pee in a better location. Actually, they often do that themselves because they would rather pee on better turf and for a while it was too cold to be picky.