ISSN 2398-2977      

Physical urticaria

pequis

Synonym(s): Hives


Introduction

  • Cause: non-immunologic specific external stimuli such as pressure, heat, cold and exercise.
  • Signs: multifocal to coalescent edematous lesions (wheals) with or without pruritus.
  • Diagnosis: history, clinical examination, reproducibility, exclusion of differentials.
  • Treatment: avoidance of the primary stimulus, anti-inflammatory treatment (antihistamines, corticosteroids and fatty acids), allergen specific immunotherapy.
  • Prognosis: excellent if the specific cause is eliminated.

Pathogenesis

Etiology

  • Pressure-induced urticaria: dermatographism Dermatographism.
  • Cold urticaria:
    • Most often in cold climates.
    • Direct exposure to cold (non-blanketed areas).
  • Cholinergic (heat-induced) urticaria:
    • Increase in body temperature.
    • May follow intense exercise.
    • Bathing in hot water.
    • In humans, subtypes of this disease can lead to hypohidrosis or anhidrosis, this may be similar in horses with anhidrosis, but no literature supports this speculation yet.
  • Non-cholinergic exercise-induced urticaria:
    • Elicited by exercise only.
    • Hot bathing does not cause the cutaneous reaction.
    • Some cases of ‘stress-induced urticaria’ in Thoroughbreds may be triggered by specific foods (food-dependent) administered few hours before the exercise.
  • Vibrational urticaria:
    • Associated with transport of the horse.
    • Exclusion of other possible causes (allergens or irritants within the trailer).
    • Cleaning the trailer or changing trailer does not prevent the formation of wheal during transport.
  • Solar-induced urticaria: reported in humans but not in horses.

Predisposing factors

General

  • It is often difficult to identify underlying factors that predispose horses to physical urticaria.
  • Consider food reactions and drug reactions.
  • Environmental factors can also sensitize horses.

Specific

  • Very difficult to identify specific underlying cause.

Pathophysiology

  • Regardless of the cause, mast cell degranulation occurs. Sensitization by IgE is suspected in humans.
  • Basophils, macrophages and other cells release bioactive molecules, eg histamine, platelet-activating factor and prostaglandins.
  • Their effects include vascular smooth muscle relaxation and retraction of endothelial cells that result in plasma extravasation → edema (wheal).
  • In severe cases serum exudation with crusting and subsequent hair loss.

Timecourse

  • Usually minutes after inciting stimuli.
  • Duration from few hours to days.

Epidemiology

  • It is often (but not always) limited to one horse.

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.
  • Rashmir-Raven A M (2019) A review of physical urticarias in the horse. Equine Vet Educ 31 (4), 195-197 VetMedResource.
  • Pilsworth R C & Knottenbelt D (2007) Skin diseases refresher urticaria. Equine Vet Educ 19 (7), 368-369 WileyOnline.

Other sources of information

  • Fadok V A (2014) Equine Urticaria. In: Veterinary Allergy. Eds: Noli C, Foster A & Rosenkrantz W. Wiley Blackwell, UK. pp 338-343.
  • Scott D W & Miller W H Jr (2011) Skin Immune System and Allergic Skin Diseases. In: Equine Dermatology. 2nd edn. Saunders, USA. pp 263-313.
  • Knottenbelt D C (2009) Immune-Mediated/Allergic Diseases. In: Pascoe’s Principles and Practice of Equine Dermatology. 2nd edn. Saunders, USA. pp 253-297.

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