Diagnosis
This patient has urticaria (hives), presenting as variously shaped wheals on his chest and arms, resulting from a drug allergy.
These wheals are erythematous, nonpitting, edematous plaques that change size and shape by peripheral extension or regression. Urticaria is a dynamic process in which new wheals evolve as old ones resolve. Wheals result from localized capillary vasodilation, followed by transudation of protein-rich fluid into the surrounding skin. The wheals resolve when the fluid is slowly reabsorbed.
Urticaria symptoms and signs
Itching is the hallmark symptom of urticaria. Patients may also experience burning or stinging. Acute urticaria may exhibit a rapid or gradual onset. The onset and resolution of wheals vary with the cause, and vary even among persons who have the same underlying cause.
It is easier to determine the precipitating factor—a drug allergy in this case—with acute urticaria than chronic urticaria (lasting 6 or more weeks). Angioedema causes a deeper edematous area that involves transudation of fluid into the dermis and subcutaneous tissue.
Wheals vary in size from the small, 2-mm papules of cholinergic urticaria to giant hives that may cover an extremity or part of the abdomen in a single wheal. The wheal may be all red or white, or the border may be red with the remainder of the surface white. Wheals may be surrounded by a red halo. The larger lesions (over 5 mm in diameter) are called plaques. In patients with darker skin, the wheals may be skin-colored only, with no visible erythema.
Differential diagnosis
The full differential diagnosis of urticaria includes angioedema, insect bites, food allergies, erythema multiforme, bullous pemphigoid, dermatitis herpetiformis, urticarial contact dermatitis, pruritic urticarial papules and plaques of pregnancy (known as PUPPP), mast cell releasability syndromes, and urticarial vasculitis.
Food allergies and insect bites can sometimes cause urticarial reactions. Angioedema is seen more often on the face and is especially found around the mouth and eyes.