Assessment of rash in children

Childhood rashes are cutaneous eruptions of acute onset. Clinically, they may be categorised as maculopapular, pustular, vesiculobullous, diffuse/erythematous, or petechial/purpuric in nature. However, in many aetiologies these forms may co-exist or evolve from one form to another.

Initial considerations in evaluating a rash in children include its morphology, duration, and distribution. Age, sex, family history, medications, known allergies, and exposures are also of primary importance.

Generally, rash in the absence of fever or systemic symptoms is not urgent. However, when fever or signs of illness are present, urgent evaluation and treatment must be considered. The differential diagnosis is extensive, ranging from self-limiting conditions (e.g., roseola) to life-threatening illnesses such as meningococcal disease.

Several systemic conditions with a serious clinical course may have a rash as a component and should be assessed urgently if suspected (see Urgent considerations).

Definitions

• Macule: a flat area of colour change <1 cm in size (e.g., viral exanthem [such as measles and rubella], morbilliform drug eruption).

• Patch: a large macule >1 cm in size (e.g., viral exanthem [such as measles and rubella], morbilliform drug eruption).

• Papule: a raised area <1 cm in size (e.g., wart).

• Nodule: a larger papule, >1 cm in size (e.g., nodular prurigo).

• Plaque: a flat-topped raised area (a cross between a nodule and a patch; e.g., psoriasis).

• Vesicle: a small fluid-filled lesion (blister) <0.5 cm in size (e.g., varicella, eczema herpeticum).

• Bulla: a larger vesicle >0.5 cm (e.g., bullous impetigo).

• Pustule: a pus-filled lesion (e.g., folliculitis).

• Wheal: a transient raised papule or plaque caused by dermal oedema (e.g., urticaria).

• Scale: flakes of stratum corneum (e.g., eczema, psoriasis).

• Crust: dried serum, blood, or purulent exudate on the skin surface (e.g., impetigo).

• Erosion: loss of epidermis, heals without scarring (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis).

• Ulcer: loss of epidermis and dermis, heals with scarring (e.g., venous ulcer, pyoderma gangrenosum).

• Excoriation: loss of epidermis following trauma such as scratching (e.g., pruritus).

• Fissure: a split in the skin (e.g., angular cheilitis, palmoplantar keratoderma).

• Lichenification: thickening of the skin with accentuation of skin markings (e.g., chronic eczema, lichen simplex chronicus).

• Purpura: an area of colour change (red or purple) due to bleeding into the skin; does not blanch on pressure (e.g., vasculitis, disseminated intravascular coagulation).

• Petechia: a pin-point purpuric lesion (e.g., vasculitis, disseminated intravascular coagulation).

• Ecchymosis: a larger area of purpura (e.g., vasculitis, disseminated intravascular coagulation).