The appropriate therapy obviously involves identification of the predisposing, perpetuating, and primary factors. In general, avoiding pastures/paddocks with mud, water, or sand may minimize predisposing factors. Keeping patients stalled during wet weather and until morning dew has dried is often rewarding. Use of alternate sources of bedding may be beneficial because the chemicals in treated or aromatic types of wood shavings may result in contact dermatitis. Lastly, clip hairs — especially feathers — to avoid moisture retention.
Perpetuating factors should be addressed according to the severity of the condition. The most conservative approach includes cleansing lesions with antimicrobial shampoos (benzoyl peroxides, chlorhexidine, ethyl lactate, imidazoles) twice daily for 7 to 10 days and then tapering in frequency. If a dry environment is not possible, the affected pastern areas can be protected with ointments (creating a moisture barrier); with padded and water-repellent bandages (changed q24-48h); or with Facilitator, a hydroxy-ethylated amylopectin liquid bandage that is replenished every 1 to 3 days. If the lesions are exudative, astringent solutions — such as lime sulfur (LymDyp), aluminum acetate solutions, black tea bag or sauerkraut poultices, or acetic acid/boric acid wipes (Malacetic Wipes, Dermapet Inc., West Plains, Mo.) — should be used after cleansing.
Topical sprays, creams, or ointments that contain antibiotics, steroids, antifungal agents, or a combination thereof may benefit the patient, depending on the diagnosis. A 2% mupirocin ointment (Bactoderm), with excellent tissue penetration, is the author’s preference for addressing localized dermatophilosis and bacterial dermatitis. A DMSO / thiabendazole / sulfa ointment has also been described in the fourth edition of Current Therapy in Equine Medicine. If generalized to all four limbs, treatment of the bacterial dermatitis is best accomplished with daily systemic antibiotics (trimethoprim/sulfa 30 mg/kg/day or cephalexin 22 mg/kg q8hrs) until 7 days after clinical resolution.
Lime sulfur dips and chlorhexidine / imidazole-containing shampoos, sprays, and residual leave-on products comprise the current antifungal arsenal in veterinary medicine. Topical enilconazole (Imaverol), labeled for use in horses in various countries other than the United States, has been used to treat fungal infections with reported success. Many veterinary dermatologists feel that systemic griseofulvin lacks efficacy for the treatment of equine dermatophytosis.
Ectoparasiticidal therapy consists of avermectins, topical organophosphates (malathion, coumaphos), pyrethroids (permethrin, flumethrin), lime sulfur, and fipronil (Frontline). The latter has had recent success in the treatment of Chorioptes bovis within a group of heavier cob and draught-cross horses. Of note was the ability of the parasite to survive off the host, enduring solely in the presence of skin debris in a moist and dark environment and thus emphasizing the need for environmental management to prevent recurrence.
Immunomodulators have been used for the condition. Interferon-a2a given at 1000 IU/ml on a cycle of 1.0 ml per horse daily for 3 weeks and then off for 1 week has been used by the author to help stimulate the local immune defense system, with very little cost or side effects. Immune-mediated conditions such as PLV, however, require a significant immunosuppressive effort to achieve resolution and control of the clinical signs. High-dose glucocorticoids, preferably dexamethasone (0.1-0.2 mg/kg q24h for 7-14 days, then taper over the next 4-6 weeks), along with reduction of UV light exposure by stabling or covering with a light bandage, appears to control — if not resolve-many cases. Should resolution of clinical signs not be achieved by 14 days, the author has achieved excellent results by adding pentoxifylline (PTX), a phosphodiesterase inhibitor. PTX has been reported to have multiple immunomodulatory effects that potentiate the effectiveness of traditional immunosuppressive drugs (i.e., steroid-sparing effect). These include inhibition of lymphocyte activation and proliferation; increased lymphocyte suppression; suppression of tumor necrosis factor (TNF)-a, lymphotoxin, and interferon-7 production; and upregulation of IL-10 mRNA that leads to increased IL-10 serum levels. Oral absorption varies considerably between individuals; thus reported dosages range between 4 to 8 mg/kg every 12 hours.
Once the skin has returned to normal, long-term control of PLV may be achieved by a combination of topical steroids (betamethasone valerate 0.1%, aclometasone 0.05%), coupled with an every other day systemic regimen of PTX and, if necessary, low-dose dexamethasone on an alternate day basis.
The prognosis and healing time of equine pastern dermatitis depends on the stage of disease when treatment begins and on the ability to identify the etiology. Ensuring that predisposing, primary, and perpetuating factors are encompassed in a diagnostic and treatment plan will optimize the likelihood of a positive outcome.