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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • A variety of inflammatory skin conditions of the horse's distal extremity. Considered as a “syndrome or cutaneous reaction pattern” of the plantar/palmar aspects of the pastern and bulbs of the heels but may extend proximally to the mid-cannon
  • “Grease heel” is not a specific disease entity

Pathophysiology!!navigator!!

Dermatitis is preceded by mechanical injury to the stratum corneum. Mechanical irritants include chronic moisture; frictional injury from bedding, tack, arenas, and track soils; ectoparasites; and microorganisms. Inflammation of the epidermis, dermis, and adnexa gives rise to crusts, scale, erosion, ulceration, alopecia, lichenification, fibrosis, exuberant, verrucous masses representing granulation tissue, and scarring.

Systems Affected!!navigator!!

Skin/exocrine.

Genetics!!navigator!!

Genetics may play a role, as anatomic features correlate with disease severity in draft horses.

Incidence/Prevalence!!navigator!!

  • The most prevalent form of the disease is mild
  • True incidence is unknown

Geographic Distribution!!navigator!!

Worldwide

Signalment!!navigator!!

  • Occurs in all breeds but most common in heavy draft horses
  • Mean age of onset is 9 years—range 2.5–26 years of age
  • No reported sex predilection

Signs!!navigator!!

  • Variable and dependent on the etiology and the stage of disease
  • Bilateral symmetrical involvement of the caudal pastern of the hind limb is the most common presentation. Can be unilateral
  • Signs begin on the palmar and plantar aspects of the fetlocks up to the carpal and tarsal joints and may progress to the metatarsal regions. All surfaces of the limbs can be involved
  • Earliest lesions are mild scale and crusts with erythema, edema, exudation, matted fur, and alopecia. Other features are hyperkeratosis with hyperplastic plaque lesions and scaling
  • Verrucous masses, referred to as “grapes,” have rugged surfaces with fissures, scale, crusts, excoriations, erosion, ulceration, and varying degree of greasiness, malodor, and exudate
  • In advanced cases, removal of thick adherent scale and crusts can cause significant pain, erosion, and ulceration. Serosanguineous or suppurative exudate is associated with erosion, ulceration, crusts, or the presence of vasculitis on nonpigmented limbs
  • Distal limb edema, cellulitis, and fissuring of hyperplastic skin can cause reluctance to ambulate
  • Varying degrees of pruritus are present in all stages depending on the etiology. Distal extremities with white stockings may be more affected

Causes!!navigator!!

Pastern dermatitis has numerous potential causes.

  1. Factors that provide the basis for thedevelopmentof pastern dermatitis
    • In heavy draft horses
      • Circumference of cannon
      • Prominence of fetlock tufts of hair, chestnuts, ergots, and, if present, prominent bulges in the fetlock region
      • Poor hoof condition
    • Chronically moist conditions, abrasion from plants in the pasture or irritants in the soils of tracks or riding areas, sand, or beddings
    • Poor stable hygiene
    • Use of irritant topical products, training devices, or treated bedding
    • Keratinization disorder
  2. Factors thatinitiatedermatitis are considered primary disease etiologies
    • Parasitic
      • Chorioptes spp.
      • Trombiculidiasis
      • Pelodera strongyloides
      • Strongyloides westeri larvae
      • Habronemiasis
    • Infectious
      • Dermatophytosis
      • Mycetoma
      • Sporotrichosis
      • Spirochetosis
    • Immune mediated
      • Contact hypersensitivity
      • Photoactivated vasculitis
      • Leukocytoclastic pastern vasculitis
      • Cutaneous drug reaction
      • Pemphigus complex
      • Bullous pemphigoid
    • Iatrogenic
      • Blistering agents
      • Pin firing
      • Scald from urine or feces
      • Wire injury
    • Neoplastic
      • Fibroblastic or verrucose sarcoid
      • Squamous cell carcinoma
      • Cutaneous lymphoma
  3. Features of the dermatitis thatmaintain, reinforce, and strengthen the disease process
    • Bacterial
      • Staphylococcus spp., Corynebacterium spp., fusiform bacteria, botryomycosis infections
      • Dermatophilus congolensis
    • Environmental
      • Overvigorous washing and scrubbing
      • Application of occlusive ointments and dressings over necrotic skin and crusts
      • UV light exposure
      • Insect bites
    • Chronic pathologic changes

Risk Factors!!navigator!!

Risk factors are predisposing factors that increase susceptibility:

  • Environmental—climate (more common in the winter), moisture, and stable and pasture hygiene
  • Iatrogenic—adverse reactions to topical medications, use of splint boots
  • Genetic—excessive hair or feathering on pastern, keratinization defect

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Diagnosis is based on history, physical examination, and findings from diagnostic tests.

Additional differentials:

  • Chronic progressive lymphedema
  • Exfoliative eosinophilic dermatitis and stomatitis

CBC/Biochemistry/Urinalysis!!navigator!!

  • Perform if photosensitization, hepatopathy, or vasculitis is suspected
  • Use to screen for metabolic disorders

Other Laboratory Tests!!navigator!!

  • Surface cytology with Diff-Quik® stains collected from erosions or ulcers shows a neutrophilic exudate with intra- and/or extracellular cocci and represents secondary folliculitis
  • Skin scrapings to rule out ectoparasites
  • Bacterial and dermatophyte cultures to determine bacterial species and susceptibility and/or dermatophyte infections

Imaging!!navigator!!

Radiographs may rule out other causes of lameness.

Other Diagnostic Procedures!!navigator!!

Obtain skin biopsies by wedge resection or double-punch technique in horses with marked hyperkeratosis or nodular or proliferative changes. Biopsies are essential for confirmation of pastern dermatitis due to immune-mediated or neoplastic disease, keratinization disorders, vasculopathies, or contact hypersensitivities.

Treatment ⬆ ⬇

Outline

TREATMENT

Aims!!navigator!!

The primary goal is to establish and eliminate factors in the 3 categories of the disease process. No single therapy applies to all cases owing to the variability of cause and clinical consequences.

Appropriate Health Care!!navigator!!

Outpatient medical management is appropriate for most cases.

Nursing Care!!navigator!!

  • Debridement—remove all necrotic and contaminated tissues, keep the skin dry and free of irritation during treatment. Debridement may require sedation as severe cases are usually painful. Remove excess hair. Simple hydrotherapy with the application of an antimicrobial, keratolytic, and keratoplastic shampoo is used in the initial debridement
  • In mild cases, a conservative approach of cleansing lesions every 12 h for 7–10 days may be all that is needed
  • In moderate to severe cases, debridement is performed using creams with benzoic or salicylic acids and propylene glycol applied to the lesions, covered with thin plastic film, and wrapped with a lightly padded clean stable bandage for 12 h. Remove the dressing and gently wash with a mild antimicrobial shampoo. If crusting is still present, repeat the process. Assess the degree and depth of ulceration. Severely ulcerated skin will not heal if exposed to repeated wetting and trauma
  • For exudative lesions, astringent solutions, such as Burow's solution, can be applied to the area every 8–12 h for 10 min; alternatively, soak the leg in an astringent solution for 15–30 min. Before application of astringent, wash extremities with an antimicrobial shampoo
  • If providing a dry environment is not possible, consider applying a light barrier cream, such as petroleum jelly or liquid bandages

Activity!!navigator!!

  • Rest from work. Avoid areas that are wet, muddy, sandy, or have an abundance of sharp protruding roughage that initiates epidermal microtrauma. Keep in clean dry stall during wet weather
  • If predominantly white legs are affected—suggestive of solar or photoactivated dermatitis; keep out of UV light until a definitive diagnosis is made

Diet!!navigator!!

N/A

Client Education!!navigator!!

  • Warn owners and plan for recurrence
  • Describe multifactorial nature of the disease

Surgical Considerations!!navigator!!

Surgical or cryosurgical intervention of exuberant granulation tissue may be required.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • For localized bacterial dermatitis, consider topical antimicrobials that penetrate the epidermis such as silver sulfadiazine or 2% mupirocin ointment, applied every 12 h for 2 weeks past clinical cure. Other effective topicals include 2–4% chlorhexidine sprays and mousses, Mud Stop® (UK), and products containing Kunzea oil
  • For mild to deep bacterial dermatitis involving all 4 legs, use systemic antimicrobials, such as trimethoprim-potentiated sulfonamides (sulfadiazine or sulfamethoxazole) 30 mg/kg PO every 12–24 h until 2 weeks past clinical cure. Use in conjunction with antimicrobial shampoos and sprays to hasten resolution
  • Dermatophytosis—topical rinses, sprays, shampoos, leave-on mousses such as 2% lime sulfur, 2% miconazole/climbazole with 2–4% chlorhexidine and 2% enilconazole can be used.
  • Ectoparasiticides—topical pyrethroids, 5% lime sulfur solution, and 0.25% fipronil spray. Fipronil spray may reduce chorioptic mange but may not eliminate it. Apply 125 mL of spray from elbow, stifles downward to each leg. Reapply in 3 weeks. Treat all animals in contact with the infected animal simultaneously. Infestation with Chorioptes requires environmental decontamination as mites live off the host for up to 70 days. Topical eprinomectin solution at 500 µg/kg once weekly for 4 weeks was shown to be effective for psoroptic mange
  • Judicious use of systemic steroids is indicated to reduce inflammation especially in idiopathic, contact, pastern leukocytoclastic vasculitis and immune-mediated conditions. Topical steroids such as triamcinolone 0.015% or hydrocortisone 1% sprays, betamethasone 1%, or mometasone 0.1% creams could be used alone or in conjunction with systemic steroids to decrease the dose needed with systemic therapy alone

Contraindications!!navigator!!

Overzealous application of topical ointments on the surface of necrotic skin and crusts.

Precautions!!navigator!!

None

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

None

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Dependent on disease severity.

Prevention/Avoidance!!navigator!!

  • Prevention relies on avoidance. Wet grass in the early summer morning can macerate the epidermis. Recurrent cases benefit from stalls with clean, dry bedding. Simple avoidance of UV light may not be sufficient to prevent disease
  • Application of a light barrier cream before exercise, combined with cleansing and drying after exercise, may prevent recurrence
  • Asymptomatic carriers of dermatophytosis or Chorioptes need treatment

Possible Complications!!navigator!!

Lameness

Expected Course and Prognosis!!navigator!!

Prognosis depends on the stage of the disease.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

N/A

Age-Related Factors!!navigator!!

Severity may worsen with age.

Zoonotic Potential!!navigator!!

Dermatophilosis, dermatophytosis, and Chorioptes are zoonotic.

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

  • Grease heel—early form
  • Scratches—early form; colloquial term

Suggested Reading ⬆ ⬇

Psalla D, Rufenacht S, Stoffel MH, et al. Equine pastern vasculitis: a clinical and histopathological study. Vet J 2013;198:524–530.

Author(s) ⬆ ⬇

Author: Gwendolen Lorch

Consulting Editor: Gwendolen Lorch

Additional Further Reading ⬆

Click here for Additional Further Reading