Urticaria causes and treatment

Urticaria is associated with raised dermal welts caused by histamine release.

Aetiology and pathogenesis

Allergens, infectious agents or other triggers cause mast cells and basophils to release histamine and other inflammatory mediators. These mediators cause vasodilatation, plasma extravasation and nerve activation, which result in weals, erythema and sometimes pruritus. Common triggers of urticaria are vaccines, insects, foods and drugs.

the head and trunk of a food-allergic Dalmatian.

Fig. 2.23 Pruritus, urticaria and folliculitis on the
head and trunk of a food-allergic Dalmatian.

Clinical features

Short-haired dogs appear to be predisposed to urticaria. Females may also be predisposed. Raised domes or plaques sometimes coalesce into serpiginous patterns on the skin. The oedematous skin causes the hair to stand erect in short-haired dogs. Urticarial lesions are commonly erythematous and sometimes pruritic (Fig. 2.23). This reaction can occur with other signs of anaphylaxis such as angio-oedema of the legs, face or ears (Fig. 2.24), vomiting, diarrhoea, collapse, hypotension, respiratory distress, heart failure and death. Urticaria can be acute or chronic. Lesions blanch when pressed.

Dog has Urticaria and angio-oedema

Fig. 2.24 Urticaria and angio-oedema in a Boxer
following methadone administration.

Differential diagnoses

  1. Bacterial folliculitis.
  2. Vasculitis.
  3. Erythema multiforme.
  4. Cutaneous histiocytosis.
  5. Staphylococcal folliculitis

 

Diagnosis

Lesions are usually easily recognisable. Biopsy with histopathology should be performed for chronic or unresponsive lesions to rule out other causes.

Treatment

• If known, causative agents should be avoided.

• Most cases of urticaria resolve spontaneously in 12–48 hours.

• Acute and severe patients should be monitored in the clinic until weals begin to resolve and the patient is showing no signs of developing anaphylaxis.

• Owners should be instructed on how to monitor for signs of anaphylaxis.

• Adrenaline (1:1000 0.1–0.5 ml sc or im) will help reverse symptoms if the dog is showing any other signs of anaphylaxis.

• Dexamethasone (0.05–0.1 mg/kg iv) works rapidly to resolve urticaria, pruritus and erythema. Usually, only one dose is needed.

• Prednisone (1 mg/kg po q24 h and taper) for 3–5 days is typically curative within a day or two.

• Oral or injectable steroids can be combined with antihistamines such as diphenhydramine (2.2 mg/kg po q8–12 h), chlorpheniramine
(0.4 mg/kg po q8–12 h) or hydroxyzine (2.2 mg/kg po q8–12 h). Antihistamines are most helpful to prevent new lesions rather than resolve existing lesions, but are safer than prednisone for long-term use if needed.

• The treatment for chronic urticaria depends on the underlying cause; these cases should be biopsied and may need work-ups and treatments similar to vasculitis (see pages 85 and 221) and atopic dermatitis.

 

Urticaria in dogs is common and typically rapidly responsive to treatment.