Felis ISSN 2398-2950

Skin: allergic contact dermatitis

Synonym(s): Contact hypersensitivity

Contributor(s): Ian Mason, David Scarff

Introduction

  • Very rare, cell-mediated hypersensitivity reaction to contacted environmental allergens in ed individuals.
  • Contact reactions are more commonly due to irritant contact dermatitis Skin: irritant contact dermatitis than contact hypersensitivity.
  • Signs: pruritus, maculopapular dermatitis, usually affecting the sparsely haired skin in areas in contact with the allergen.
  • Diagnosis: elimination of allergen and subsequent provocative exposure, patch testing.
  • Treatment: prevention of access to offending allergens.
  • Prognosis: variable, may not be possible to identify and exclude allergen.

Pathogenesis

Etiology

  • Plant resins and oils.
  • Common medications, eg neomycin Neomycin in otic preparations.
  • Home furnishings (carpet mordants and dyes).
  • Cleaning products (detergents, polishes).
  • Chlorine in water.
  • Common flea collars (leather collars).
  • Insecticides.
  • Cat litter additives.
  • Plants (Commelinanceae family).

Predisposing factors

General

  • Topical application of medication or flea collar.
  • Site of skin.
  • Age of skin.
  • Degree of hydration.
  • Local environment of skin.

Specific

  • Overhydration of the corneum, eg occlusion or prolonged wetting.
  • pH (alkaline encourages penetration).
  • Lipophilicity (may be absorbed through the sebaceous gland or root sheath).
  • Ability to provoke inflammation (inflammation increases epidermal permeability).

Pathophysiology

  • Rare in the cat due to regular grooming and removal of foreign proteins. Also as hair coat over much of body.
  • In the dog, chemicals act as haptens to bind to proteins   →   a conjugate   →   binding to Langerhans cells in the skin   →   initiation of a T-cell response. Following exposure to antigen in a ed animal, mononuclear cells infiltrate the skin. These are removed by ed lymphocytes leaving intraepidermal vesicles. This type IV hypersensitivity reaction leads to pruritus (not yet proven in the cat).
  • An immediate hypersensitivity reaction may also be involved.
  • Low molecular weight haptens link epidermal proteins to form antigens. Antigen is trapped, processed and presented by Langerhans' cells. They produce cytokines which attract T-cells, leading to activation of keratinocytes to release proinflammatory cytokines. They also travel to local lymph nodes to amplify the immune response .

Timecourse

  • Sensitization takes a minimum of 3 weeks, more commonly >2 years.
  • After contact with an allergen, clinical signs will take 48 hours approximately to develop in a sensitized cat (a delayed allergic reaction).

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Marsella R, Kunkle G, Lewis D (1997) Use of pentoxifylline in the treatment of allergic contact reactions to plants of the commelinanceae family in dogs. Vet Derm (2), 121-126 Wiley Online Library.
  • Conroy J D (1983) An overview of immune-mediated mucocutaneous diseases of the dog and cat. I. Diseases based on allergic reactions. Am J Dermatopathol (5), 505-509 PubMed.
  • Austin V H (1979) Alopecias of the dog and cat. Part II. Mod Vet Pract 60 (2), 130-134 PubMed.
  • Scott D W (1978) Immunologic skin disorders in the dog and cat. Vet Clin North Am (4), 641-664 PubMed.


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