Table 1.

Distinguishing features of annular urticaria, erythema multiforme, and serum-sickness-like reactions.

Feature	Annular urticaria	Erythema multiforme	Serum-sickness-like reactions	Urticarial vasculitis
Appearance of individual lesions	Annular and polycyclic wheals with central clearing or ecchymotic centres	Classic target lesion with purpuric or dulsy, violaceous centre (may blister), middle ring of pallor and edema, outer ring of erythema or blisters	Polycyclic urticarial wheal with central clearing, may appear purpuric	Hives with dusky purpuric centre
Location	Trunk, extremities, face	Involvement of palms, soles common	Trunk, extremities, face, lateral borders of hands and feet	Trunk, extremities, face, lateral borders of hands and feet
Duration of individual lesions	<24 h	Days to weeks	Days to weeks	Days to weeks
Fixed lesions	No	Yes	Yes	Yes
Total duration of rash	2–12 days	2-3 weeks	1–6 weeks	1–6 weeks
Mucous membrane involvement	Oral edema common, no erosions or blisters	May see oral erosions or blisters of lips, buccal mucosa, and tongue, rarely involves conjunctiva, nasal, or urogenital mucosa, usually involving only a single site	Oral edema common, no erosions or blisters	May see oral erosions or blisters of lips, buccal mucosa, and tongue, may involve conjunctiva, nasal, or urogenital mucosa, may involve several sites
Facial or acral edema	Common	Rare	Common	Common
Dermographism	Yes	No	No	No
Fever	Occasionally, low grade	Occasionally, low grade	Prominent, high grade	Variable
Associated symptoms	Pruritus	Mild pruritus or burning	Myalgias, arthralgias, lymphadenopathy	Variable
Common triggers	Viral illness, antibiotics, immunizations	Herpes simplex virus, other viral illness	Antibiotics	Infections, autoimmune processes, neoplastic processes, drugs
Treatment	Discontinue any new or unnecessary antibiotics or medications, combinations of H1 and H2 antihistamines may be helpful, systemic steroids can be helpful in more recalcitrant cases	Supportive care, early institution of systemic steroids can sometimes be helpful	Discontinue any new antibiotics or medications, H1 and H2 antihistamines, supportive care, consider systemic steroids	Discontinue any new antibiotics or medications, H1 and H2 antihistamines, supportive care, consider systemic steroids