White Line Disease in Horses
(Hollow wall, Seedy toe, Onychomycosis)
In white line disease, the hoof wall separates from the underlying laminae (stratum internum) at the level of the stratum medium (tubular horn). The separation likely starts as a result of abnormal wall stress due to poor foot conformation or trimming (eg, long toe, underrun heels) and can start at the toes, quarters, or heel. Opportunistic bacteria and fungi may be present in the fissures in the hoof wall. The outer surface of the wall may appear sound, but on dressing the foot from the solar surface, there is commonly a separation of the hoof wall from the underlying laminae. Tapping on the outside of the wall at the toe elicits a hollow sound over the affected portion. Lameness may be present in severe cases, in which loss of support of the distal phalanx results in displacement similar to that seen in laminitis.
The diagnostic evaluation includes a thorough physical examination and lateral and dorsopalmar radiographs to assess the extent of separation of the hoof wall and any displacement of the distal phalanx. For treatment, corrective trimming is critical to remove abnormal stresses on the hoof wall, followed by removal of the entire extent of the separated hoof wall to the point that firm, healthy adhesion of the hoof wall to the underlying stratum internum can be seen. This hoof wall debridement is performed with a combination of hoof nippers, hoof knives, and possibly a rotary tool. With proper debridement, there may be no need for antiseptic or astringent treatment. However, topical treatment with tincture of iodine is commonly performed daily for at least a week. Additionally, commercial equine foot formulations that produce chlorine dioxide can also be used. Corrective shoeing is critical to provide adequate support to the remaining foot, while removing stress from the affected regions; a heart bar or egg bar shoe in combination with a resilient putty in the caudal two-thirds of the sole (to provide distal phalanx support) may be necessary if displacement of the distal phalanx is a concern.