WL separation is that is caused by flare. Flare walls cause stretching of the white line which can lead to separation of the white line (dead laminae) and then leaves the hoof vunerable to abscessing either in the wall or the bar. When I trim an abscessed hoof, I see what we have come to term as WLD. But as I said, it's not diseased, it's dead.
When a hoof is affected by an abscess in an overgrown bar (bar is an extension of hoof wall) the abscess often invades the much of, or the entire hoof. Abscesses can cause problems in a hoof for years if the horse is shod and even after it goes barefoot can take years to completely fester out. Not usually, but I have seen that situation and the cause if typically flare.