The key to successful diagnosis of a red rash or swelling is a careful history and physical examination while keeping a broad list of differential diagnoses in mind. Timing, appearance, and progression of the rash; presence of associated signs and symptoms; and recent exposures and activities aid in identifying the etiology and diagnosis. The distribution, appearance, and feel of the skin are also helpful in determining the etiology.

• Lesions that change in location, shape, and size over minutes to hours are likely urticarial. They can be caused by an exposure to a new antigen (detergent, perfume, food), but are more commonly caused by viral infections.

• Cellulitis and erysipelas are characterized by erythema and tender swelling surrounding a break in the skin, and may be accompanied by fever.

• Insect bites can be discrete or clustered and are more frequent on exposed surfaces of the skin. Time spent outdoors, near a pet, or with other similarly affected individuals is suggestive.

• A hemangioma may start off as a flat area of telangiectasia with a surrounding ring of pallor. A hemangioma typically increases in size over the child’s first months of life prior to involution.

• Hematoma should be suspected with a suggestive history or whenever there is concern for nonaccidental trauma.

• Contact dermatitis is an allergic hypersensitivity response to an irritant or allergen that is usually limited to the area where the exposure occurred and is frequently pruritic.

• Erythema infectiosum is often accompanied by fever, rhinorrhea, and/or arthralgias.

• Pityriasis rosea presents initially as a single patch (the “herald patch”) that evolves into a diffuse macular eruption. It is sometimes pruritic. Systemic symptoms are rare.

• Erythema nodosum often occurs in the setting of infection but can also be due to a wide variety of immunologic and oncologic conditions.

• Noting whether the patient has multiple, clustered, or discrete lesions can help to narrow the differential diagnosis.

• Urticarial lesions have a wheal and flare appearance that can evolve during examination.

• Cellulitis and erysipelas are typically warm and tender. Erysipelas is raised, with well-defined edges, whereas cellulitis lacks defined edges. The presence of fluctuance suggests an underlying abscess.

• Insect bites frequently have a central punctum with surrounding erythema. If multiple bites are present, they are usually grouped rather than randomly scattered.

• A subtle cluster of blanching telangiectasias with a ring of pallor is suggestive of an early hemangioma. They later develop into nonblanching cherry red macules or papules. Bluish discoloration suggests deeper involvement.

• 

Stay updated, free articles. Join our Telegram channel

Join