KARA N. SHAH
DEFINITION OF THE COMPLAINT
Rash is a general term applied to any acute or chronic skin eruption, and is the presenting problem or secondary complaint for 20%-30% of pediatric visits to pediatricians, emergency rooms, and primary care practitioners. Rash is variably used to describe the dermatologic manifestations of a variety of disorders, and as most rashes are benign and many are self-limiting, patients with skin complaints may receive only cursory physical examinations and overly hasty diagnoses. However, the astute clinician should remember that cutaneous findings may indicate an underlying systemic disease, and therefore all patients presenting with a rash should receive a thorough history and physical examination.
The history is vitally important in narrowing the differential diagnosis of a rash. Since cutaneous manifestations can be the primary sign of systemic disease, general questions relating to the child’s overall health and review of systems are important. In particular, elicitation of a history of fever, pharyngitis, and joint symptoms can be helpful. Determination of age, gender, and racial or ethnic background may be useful, as some skin disorders are found only in particular age groups or are seen more commonly in specific subsets of the population. It is important to ask about any sick contacts, recent exposure to new medications, in particular antibiotics and antiepileptic medications, and travel and outdoor activities such as camping and hiking that might have served as a source for exposure to arthropod vector-borne infectious disease.
An understanding of the course of the rash is vital in formulating a differential diagnosis. Specific questions that will help narrow down the diagnosis include the following:
• What was the progression of the rash over time and the duration of the rash?
— Viral exanthems often manifest predictable pattern of progression. For example, measles begins at the scalp and hairline and progresses caudally, whereas scarlet fever begins on the upper trunk. Duration may be variable, but some rashes have relatively defined duration with resolution expected within a specific time.
• What is the configuration of the rash?
—The configuration or grouping or individual lesions is often very helpful. Linear or geometric configurations may be seen with allergic contact dermatitis. Herpes zoster presents in a dermatomal configuration. Annular configuration of vesicles and bullae are characteristic of linear IgA disease of childhood.
• Where is the rash distributed on the body?
—If contact dermatitis is being considered, the distribution of the rash must be consistent with the areas in contact with the inciting agent. Scabies rarely involves the face, except in infants. Atopic dermatitis favors the flexural areas of the extremities in older children.
• What is the color of the rash?
—Pigment changes can include hyperpigmentation and hypopigmentation and usually indicate postinflammatory changes due to increases or decreases in melanin production or deposition. Erythema may indicate an inflammatory process or a vascular reaction.
• What symptoms are present?
—Elicitation of symptoms, such as pain or pruritis, can be very helpful. Cellulitis is typically painful, while contact dermatitis, which is often misdiagnosed as cellulitis, is usually pruritic.
Although the presenting concern may appear to involve only the skin, it is important to thoroughly examine the hair, nails, and mucous membranes (including the oropharynx and conjunctivae) in all patients. Appropriate lighting is essential, and the patient should be undressed whenever possible to ensure that the entire skin surface area is examined. The skin examination should include not only a visual examination of the skin but palpation as well.
When evaluating a rash, it is important to differentiate between primary and secondary lesions. The primary lesion is the most representative lesion and arises from the disease process itself without alteration by patient manipulation, evolution of the underlying process, or by therapeutic intervention. Identification of the primary lesion is the most helpful step in creating a differential diagnosis. Secondary lesions result from changes caused by the patient, by the natural evolution of the pathophysiologic process, or by other influences such as application of topical medications or secondary infection. Therefore, in any given patient, there may be lesions of different morphologies, including that of the primary lesion and one or more distinct secondary lesions.
Use of correct terminology when defining the primary and secondary lesions is critical. A summary of common morphologic terms is provided in Table 9-1. A macule is a flat, nonpalpable lesion less than 1 cm in greatest diameter, while a patch is a flat lesion greater than 1 cm in diameter. Papules are raised lesions less than 0.5 cm in diameter. Nodules are larger raised lesions greater than 0.5 cm in diameter, while tumors are even larger nodules, generally over 2 cm in diameter. Plaques are well-circumscribed, raised but flat-topped lesions with a diameter usually greater than the height. Wheals are raised, edematous papules and plaques that are transient in nature. Vesiclesare raised, fluid-filled lesions less than 1 cm in diameter, while bullae are similar but greater than 1 cm in diameter. Pustules are raised well-demarcated lesions containing purulent material. Cysts are circumscribed tumors which may be fluid filled or solid. Erythema refers to an area of blanchable redness. Telangiectasia are small, superficial, blanchable dilated capillaries. Petechiae are caused by the leakage of blood into the skin from damaged capillaries and appear as pinpoint areas of nonblanchable erythema. Purpura is the leakage of blood into the skin such as may occur from damage to larger blood vessels and appears as either nonblanchable red-to-violaceous patches (nonpalpable) or papules and plaques (palpable). Burrows are linear papules caused by the movement of parasites in the superficial layers of the skin. Annular lesions present as round patches or plaques with central clearing, whereas arciformlesions are arc-like or semicircular; both may be seen in urticaria.
TABLE 9-1. Common morphologic patterns of dermatologic disease.
Secondary lesions include scales, which represent accumulation of dried layers of squamous cells. Scales can appear greasy, yellow, white, or silvery. Crusts are composed of dried exudate, which may be hemorrhagic. Erosionsrepresent denuded epidermis, while ulcers signify damage of the dermis and/or subcutaneous tissue. Excoriations are usually caused by scratching, and are linear erosions. Fissures are linear clefts involving the epidermis and dermis. Lichenification refers to an exaggeration of skin markings that result from chronic skin rubbing or scratching. A scar results from the development of dermal fibrosis that occurs after injury. Hyperkeratosis describes the development of thick and adherent scale. Atrophy is the loss or thinning of the epidermis or dermis and often presents as depressed areas of skin with translucency and/or a cigarette paper-like appearance. Additionally, there are two terms that define a constellation of findings rather than primary or secondary lesions. Eczematous lesions are erythematous, inflammatory patches, and plaques that have poorly defined borders and, when acute, may develop vesiculation and exudate. Scaling and crusting may also be present. Lichenoid refers to violaceous, flat-topped papules, often with a fine, silvery scale.
Once the primary and any secondary lesion morphology has been identified, a differential diagnosis can be generated. In dermatology, skin disease may be broadly classified into one of several categories as defined by morphology and/or pathophysiology, including papulosquamous, vesicobullous, exfoliative, eczematous, hypersensitivity, and vascular dermatoses.
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