The acutely ill patient with fever and rash may present a diagnostic challenge for physicians. However, the distinctive appearance of an eruption in concert with a clinical syndrome can facilitate a prompt diagnosis and the institution of life-saving therapy or critical infection-control interventions. Representative images of many of the rashes discussed in this chapter are included in Chap. 14.
APPROACH TO THE PATIENT: Fever and Rash
A thorough history of patients with fever and rash includes the following relevant information: immune status, medications taken within the previous month, specific travel history, immunization status, exposure to domestic pets and other animals, history of animal (including arthropod) bites, recent dietary exposures, existence of cardiac abnormalities, presence of prosthetic material, recent exposure to ill individuals, and exposure to sexually transmitted diseases. The history should also include the site of onset of the rash and its direction and rate of spread.
A thorough physical examination entails close attention to the rash, with an assessment and precise definition of its salient features. First, it is critical to determine what type of lesions make up the eruption. Macules are flat lesions defined by an area of changed color (i.e., a blanchable erythema). Papules are raised, solid lesions <5 mm in diameter; plaques are lesions >5 mm in diameter with a flat, plateau-like surface; and nodules are lesions >5 mm in diameter with a more rounded configuration. Wheals (urticaria, hives) are papules or plaques that are pale pink and may appear annular (ringlike) as they enlarge; classic (nonvasculitic) wheals are transient, lasting only 24 h in any defined area. Vesicles (<5 mm) and bullae (>5 mm) are circumscribed, elevated lesions containing fluid. Pustules are raised lesions containing purulent exudate; vesicular processes such as varicella or herpes simplex may evolve to pustules. Nonpalpable purpura is a flat lesion that is due to bleeding into the skin. If <3 mm in diameter, the purpuric lesions are termed petechiae; if >3 mm, they are termed ecchymoses. Palpable purpura is a raised lesion that is due to inflammation of the vessel wall (vasculitis) with subsequent hemorrhage. An ulcer is a defect in the skin extending at least into the upper layer of the dermis, and an eschar (tâche noire) is a necrotic lesion covered with a black crust.
Other pertinent features of rashes include their configuration (i.e., annular or target), the arrangement of their lesions, and their distribution (i.e., central or peripheral).
For further discussion, see Chap. 18.
CLASSIFICATION OF RASH
This chapter reviews rashes that reflect systemic disease, but it does not include localized skin eruptions (i.e., cellulitis, impetigo) that may also be associated with fever (Chap. 26). The chapter is not intended to be all-inclusive, but it covers the most important and most common diseases associated with fever and rash. Rashes are classified herein ...