White Line Disease is characterized as an opportunistic infection between the non-pigmented stratum medium and stratum internum (2 layers of the hoof wall). This infection is different than laminitis because it affects a more superficial layer of the hoof wall. No specific bacteria or fungus has been consistently identified as the cause of disease, it appears that environmental pathogens take advantage of a "potential space" in the hoof wall and gradually work from the ground to the coronary band.
While the root cause is different than laminitis which begins in the soft tissue layers of the foot, White Line Disease can create a mechanical form of laminitis. The disease compromises the structural integrity of the foot and rotation or displacement can be secondary to the main disease process.
White Line Disease can be difficult to recognize clinically, most horses are not lame until there is significant compromise to there hoof structure. The disease may initially present as some separation at the hoof wall /sole junction which can insidiously progress up the hoof wall. Recognizing the separation is important, radiographs are often used to characterize the more severe cases while your farrier may resect small portions of hoof wall as part of a routine trim.
In severe cases the structural integrity of the foot needs to be carefully evaluated and managed before a resection is performed. Generally the disease process resolves when the affected area is exposed to air and treated with an appropriate topical therapy.