Vascular Reactions (Morphologic Group)

Urticaria

Urticarial lesions often enlarge centrifugally. The center of such lesions fades, leaving a ring-like border. Both partial and full rings can be seen. Tremendous variation in size occurs; coalescence of two or more small rings leads to the formation of larger lesions with gyrate or serpiginous borders. No scale is present. The color varies from pink to red. Lesions may occur anywhere on the body. The rapidity with which the lesions appear, expand, and resolve is highly characteristic for urticaria. Lines drawn around lesions at any one point in time will no longer correspond to the new positions of lesions when the patient is examined several hours later. A diagnosis of urticaria is made on a clinical basis; biopsy is not particularly of help.

Erythema Multifarme

At least a few annular lesions are likely to be found in patients with erythema multiforme. Those lesions that occur distally on the extremities are more likely to be annular than are those on the trunk. Most annular lesions in erythema multiforme will be formed of two concentric rings arranged around a central bull's-eye. Such target lesions are pathognomonic for the disease. The annular lesions of erythema multiforme are small, seldom measuring more than 2 to 4 cm in diameter. All of these target lesions are round; no gyrate or serpiginous lesions are present. No scale is present. In questionable cases, biopsy can be of help.

Annular and Gyrate Erythemas

As the name implies, annular lesions are a constant feature of these diseases. All of the lesions present will be annular or gyrate; uniformly solid papules and plaques are not found. The number of lesions present is generally small. Sometimes, only a solitary ring is noted. The size of the annular lesions is highly variable, but most are palm sized or larger. Small lesions demonstrate slow centrifugal growth over a period of several weeks. The lesions are red, but the hues vary from pink to violaceous. A small amount of scale may be present on the inner aspect of the active border. The center of the ringed lesion may be darker in hue than the normal skin color. This color change represents postinflammatory hyperpigmentation. Biopsy is of help but is not pathognomonic.

Vasculitis

Small annular lesions 1 or 2 cm in diameter are occasionally found on the lower extremities In patients with vasculitis. The active border of these lesions is purpuric; it is violaceous and does not blanch on pressure. Often a purpuric papule, hemorrhagic vesicle, or tiny infarct is found in the center of these lesions. Scale is not present. The lesions remain stable in size; centrifugal growth is not notable. Individual lesions fade over a period of several weeks, but if the process is ongoing, new annular lesions may appear while old ones resolve. Biopsy confirms a clinical diagnosis.