- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
Urticaria and AG are common inflammatory reaction patterns resulting from mast cell and, to a lesser extent, basophil degranulation. AG is a focal or diffuse excessive accumulation of tissue fluid within the interstitium, often at gravitative surfaces, that presents as edematous swellings, which may exhibit serum leakage through the skin or hemorrhage. Urticarial reactions vary in severity from inconsequential to problems of a life-threatening nature.
The release of cellular inflammatory mediators such as histamine, platelet-activating factor, and prostaglandins contributes to increased vascular smooth muscle relaxation and endothelial cell retraction, causing plasma to extravasate and cause turgid edematous wheals. Urticaria is classified as immunologic, immediate immunoglobulin E-mediated (type I), immune complex-mediated (type III), or delayed cell-mediated (type IV) hypersensitivities, or nonimmunologic.
- Onset of lesions can be acute or peracute episodes occurring 15 min to hours post challenge. Chronic urticaria is a relapsing presentation that persists for at least 6–8 weeks. The characteristic lesion is a wheal—a flat-topped papule/nodule with steep-walled sides resulting from localized transient edema within the dermis. Pitting edema is a key clinical feature of urticaria or AG, although gyrate urticaria often does not pit. Clinical classification of urticaria relies on size and appearance
- Conventional—wheal size varies from 2–3 mm to 3–5 cm in diameter
- Papular—wheal size is uniform and small, ≈3–6 mm in diameter
- Gyrate (polycyclic)—wheals have unusual shapes such as annular, doughnut, serpiginous, aciform and can persist for months
- Giant—single or multiple wheals that range from 20 to 40 cm in diameter
- Exudative—severe dermal edema oozes from the skin, mats the hair, and causes alopecia, often mistaken for pyoderma, dermatophytosis, and pemphigus foliaceus
- Linear—firm, multiple, parallel contiguous banding patterns that can be present on the sides of trunk, shoulders, forearms, flanks, gaskins, and the cranial aspects of hocks. Often permanent and nonresponsive to steroid and antihistamine therapy. Multiple horses on farm may be affected
- AG (angioneurotic edema)—diffuse SC edema, affecting head, thorax, ventral abdomen, and/or gravity-dependent extremities
Causes are either immunologic or nonimmunologic, with the former the most common.
- Immunologic causes include:
- Insect hypersensitivity (stinging and biting insects), atopy (pollens, molds, and epidermals), food allergy
- Drugs (including vaccines, anthelmintics)
- Various others such as penicillin, tetracycline, sulfonamides, neomycin, ciprofloxacin, phenylbutazone, flunixin, phenothiazines, guaifenesin, ivermectin, moxidectin, iron, dextrans, hormones, and vitamin B complex
- Infections—bacterial (e.g. strangles, salmonellosis, botulinum,), pyoderma, cellulitis, lymphangitis, abscess, dermatophytosis, parasitic protozoal (e.g. Trypanosoma equiperdum)
- Vasculitis (immune-mediated or photo-activated)
- Contact with substance (e.g. leather soaps, conditioners, or rubber tack)
- Snakebite
- Plants (e.g. nettle and buttercup)
- Mast cell or lymphoreticular neoplasia
- Autogenous sweat
- Nonimmunologic factors include psychologic stresses, genetic abnormalities, temperature (heat, cold, or sunlight), physical (pressure or dermatographism), exercise, cholinergic, and administration of radiocontrast media and opiates
- Idiopathic—the likelihood of documenting a specific etiology of chronic urticaria is low, thus the diagnosis of “idiopathic” is common
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS