ISSN 2398-2977      

Urticaria/angiedema

pequis

Introduction

  • The horse has the highest propensity for urticaria.
  • Urticaria: swellings that pit with digital pressure, transient vascular epithelial reaction to immunogens or chemicals; +/- pruritus.
  • Angiedema: diffuse subcutaneous swellings usually associated with immediate-type hypersensitivities; +/- pruritus.
  • 50% cases have unknown/unidentified etiology.
  • Clinical manifestations vary from a minor transitory nature to a major systemic, and possibly life-threatening problem.
  • Cause:
    • Food allergy, drug allergy, sequele of infection, inhalation of pollens/chemicals; insect stings and parasitism; superficial trauma (dermatographism).
    • Vaccines.
    • Plants, eg nettles.
    • Snake-bites.
  • Signs: acute small   →   large swollen patches, may be generalized; distribution may reflect contact with allergen; chronic changes, amyloidosis.
  • Diagnosis: establish cause; physical examination and history; serology and histopathology of limited usefulness.
  • Treatment: management manipulation to avoid allergens; oral corticosteroids for immediate relief.
  • Prognosis: many cases spontaneously regress; others recur at random intervals and necessitate lengthy diagnostic protocols; depends on success in environmental management; maintenance - minimum alternate daily doses of oral corticosteroids may be required.
Print off the Owner factsheet on Lumps and bumps to give to your clients.

Pathogenesis

Etiology

Immunological

Non-immunological

  • Physical events:
    • Cold/ice packs.
    • Heat.
    • Light.
    • Exercise.
    • Trauma.

Predisposing factors

General
  • Heat and stress may precipitate or intensify urticaria.

Pathophysiology

  • Degranulation of mast cells and basophils → liberation of chemical mediators → increased vascular permeability, inflammation and protein leakage → wheals.
  • Both immunologic and non-immunologic mechanisms may trigger urticaria.
  • Non-immunologic triggers may be associated with an underlying allergic state.

Type I (immediate) hypersensitivity

  • Believed to be the immune reaction occurring in most cases of immune-mediated disease.
  • Exposure to antigen → antibody (IgE) production → binds to tissue mast cells and basophils.
  • Re-exposure to antigen → Ag binding to IgE → degranulation of mast cells → release of histamine and chemical mediators → increased vascular permeability, inflammation and protein leakage → wheal formation.

Type III (immune complex) hypersensitivity

  • May also occur associated with type I.
  • Ag-Ab complex formation → attach to walls of blood vessels → attaches complement → attracts neutrophils → tissue damage.

Clinical signs

  • Increased vascular permeability → early clinical signs of pitting edematous wheals.
  • Later infiltration by inflammatory cells → lesions may become firmer and more persistent.

Timecourse

  • Acute onset - from minutes to a few hours.
  • Lesions may also disappear rapidly.
  • Recurrence is common at random intervals.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Diesel A (2014) Equine urticaria: a clinical guide to management. In Pract 36 (6), 295-299 VetMedResource
  • Rendle D I, Durham A E, Wylie C E & Newton J R (2010) Results of intradermal testing for the investigation of atopic dermatitis and recurrent urticaria in 50 horses in the south of England. Equine Vet Educ 22 (12), 616-622 VetMedResource.
  • Pilsworth R C & Knottenbelt D C (2007) Urticaria. Equine Vet Educ 19 (7), 368-369 VetMedResource.
  • Paterson S (2000) Investigation of skin disease and urticaria in the horse. Equine Pract 22 (8), 446-455 VetMedResource.
  • Littlewood J D (1991) Urticaria - a clinical challenge. Equine Vet Educ 3 (3), 136-137 VetMedResource.
  • McGladdery A J (1991) Recurrent urticaria in a Thoroughbred stallion. Equine Vet Educ 3 (3), 126-129 VetMedResource.
  • Suter M & Fey H (1983) Further purification and characterization of horse IgE. Vet Immunol Immunolpathol 4, 454-553 PubMed.

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