Pediatric emergency medicine trisk 1304 1304
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CHAPTER 68 ■ RASH: DRUG ERUPTIONS
MELINDA V. JEN
DRUG ERUPTIONS
The spectrum of cutaneous drug eruptions ranges from the relatively benign,
where the medication can be continued if essential, to the severe, where there can
be significant morbidity and mortality. Thus, prompt and accurate diagnosis is
critical and can be lifesaving. The primary morphology of the eruption helps
guide the clinician to a diagnosis. Herein, we summarize the most salient features
of the most common drug reactions, with a particular focus upon their primary
morphologies.
URTICARIA
Urticaria (hives, wheals) consists of erythematous, edematous papules and
plaques that can coalesce into larger polycyclic, arcuate, and annular plaques (
Figs. 68.1 and 68.2 ). A key diagnostic feature is that individual lesions are
transient, resolving within 24 hours, but with new lesions appearing elsewhere.
As they resolve, purpuric macules secondary to capillary leak and
hyperpigmentation may remain. Pruritus and angioedema, particularly of the
eyelids, hands, and feet, are common.
Urticaria results from IgE degranulation of mast cells. Although the most
common cause of urticaria is infection, medications can sometimes trigger
urticaria. Urticaria typically appears within the first 2 weeks of starting the culprit
medication. Cephalosporins, β-lactam antibiotics, sulfonamides, and
anticonvulsants are common causes of drug-induced urticaria. Some medications,
such as nonsteroidal anti-inflammatory drugs (NSAIDs), may cause urticaria
through both immunologic and nonimmunologic pathways (via increased
leukotriene synthesis).
Urticaria is often confused for erythema multiforme (EM). The key features
differentiating urticaria from EM are morphology, individual lesion duration,
symptomology, and distribution. Urticaria can be annular, polycyclic, and arcuate,
but does not have the classic target appearance of EM. Additionally, urticaria
does not vesiculate, while the central areas of EM lesions may be bullous. As
noted above, individual lesions of urticaria last less than 24 hours, while lesions
of EM are fixed and take several days to resolve. If symptomatic, urticaria is
pruritic while EM may itch or burn. Urticaria can occur anywhere on the body,
