Erythema Multiforme
The clearly defined circular lesions with dusky red and white centers described in the question are most characteristic of erythema multiforme, specifically the targetoid or "iris" lesions that define this condition. 1
Diagnostic Features of Erythema Multiforme
The key distinguishing feature is the target or "iris" lesion, which consists of:
- A dark red center surrounded by a pink ring 1
- Well-demarcated circular plaques 2
- Characteristic "bullseye" appearance with central clearing 2, 3
- Predominantly acral distribution (extremities, limbs) 4, 5
These lesions are pathognomonic for erythema multiforme and differentiate it from the other conditions listed in your question. 2, 5
Why Not the Other Conditions?
Contact dermatitis presents with erythema, edema, and vesicles in areas of allergen exposure, but lacks the characteristic targetoid morphology with dusky red and white concentric rings. 6
Molluscum contagiosum presents as umbilicated papules, not circular lesions with dusky red and white centers. 1
Tinea versicolor presents as hypopigmented or hyperpigmented scaly patches, not targetoid lesions. 2
Scabies presents with burrows, papules, and excoriations in characteristic distributions (web spaces, wrists), not target lesions. 1
Critical Differentiation: Stevens-Johnson Syndrome/TEN
While both conditions can present with circular lesions, the morphology differs significantly:
Erythema multiforme features:
- Typical raised target lesions with three distinct zones 4
- Predominantly on limbs and extremities 4, 5
- Usually related to HSV infection 4
- Better prognosis with lower mortality 4
Stevens-Johnson Syndrome/TEN features:
- Flat atypical targets or purpuric macules (dark red flat lesions) 1, 7
- More widespread distribution including trunk and face 7
- Usually drug-triggered 4, 7
- Epidermal detachment and positive Nikolsky sign 1, 7
Common Triggers
The most frequent causes of erythema multiforme are:
- Herpes simplex virus (most common) 4, 5, 8
- Mycoplasma pneumoniae (particularly in children) 4, 5
- Drugs including sulfonamides, penicillins, phenytoin, allopurinol 2, 5
Clinical Pitfall
Do not confuse the "dusky erythema" of SJS/TEN with the targetoid lesions of EM. In SJS/TEN, "dusky" refers to confluent flat purpuric macules that progress to epidermal detachment 1, 7, whereas in EM, the dusky red center is part of a well-defined three-zone target with a pink outer ring and remains raised without significant epidermal necrolysis. 1, 4, 2