Dermatographism in a horse, responsive to cetirizine treatment

Summary Dermatographism is a common condition in man that occurs when pressure is applied to the skin and mast cells are triggered to release histamine, causing local urticarial lesions. This case report concerns a 4‐year‐old Quarter Horse gelding that was presented with pressure induced urticaria. Moderate pressure on the skin induced nonpruritic urticaria‐like swelling after approximately 3–5 min, which lasted for approximately 2–3 h. Initial treatment with cyproheptadine gave an incomplete response and unacceptable sedation as a side effect. On the second generation antihistamine cetirizine (0.2 mg/kg bwt twice daily), dermatographism was no longer present and no side effects occurred. Treatment was continued for 4 months, with at least three attempts to discontinue therapy resulting in recurrence of lesions within 24 h. Lesions resolved each time within 24 h of recommencing therapy. Dermatographism did not recur after the horse was moved to another location despite discontinuation of therapy. This report describes a case of equine dermatographism responsive to cetirizine.