Chapter 9. Rash

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.

Medical History

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 ...