Recognise true target lesions and mucosal severity across skin tones, identify infection-related triggers, separate erythema multiforme from Stevens–Johnson syndrome, and treat acute and recurrent disease safely.
Erythema multiforme is an acute immune-mediated eruption with characteristic fixed target lesions, usually triggered by herpes simplex infection. Lesions typically begin acrally and extend along limbs over several days. They may itch, burn or feel tender but widespread skin pain and large areas of detachment are warning signs for another severe cutaneous reaction. Episodes commonly settle within two to four weeks, while HSV-associated disease can recur several times a year and cause substantial interruption to eating, work and sleep.
The diagnostic discipline is to describe what is present before applying the label. Record whether each target is raised or palpable and has three zones, whether distribution is acral or truncal, how long an individual lesion persists, and exactly which mucosal sites are involved. Photograph representative lesions in neutral light with consent. In deeply pigmented skin, examine side lighting, texture and the grey, violaceous or brown central zone; blanching and palpation can reveal an inflammatory rim that colour alone understates.
HSV-1 and HSV-2 account for many recurrent episodes through a delayed immune response rather than direct viral infection of each target.
Respiratory and other infections occasionally precede target lesions, while severe infection-associated mucositis with sparse skin disease may fit RIME better.
Medicines can precede erythema-multiforme-like eruptions, but a painful drug-related truncal eruption demands active assessment for SJS or TEN.
When no trigger is evident, morphology and clinical course should be reviewed before labelling disease idiopathic or prescribing long-term treatment.
HSV genetic material and antigen-associated immune signalling in keratinocytes recruit a cell-mediated response after the original mucocutaneous infection.
Cytotoxic injury at the epidermal junction produces central keratinocyte death, surrounding oedema and an outer inflammatory ring that evolves into a target.
The same epithelial immune reaction can erode lips, mouth, eyes or genital surfaces even when total skin detachment remains limited.
Repeated HSV reactivation can reproduce the delayed eruption, which explains why continuous viral suppression prevents episodes more effectively than late episodic treatment.
A fixed palpable round plaque has three sharply visible zones, often with a dusky vesicular centre and oedematous middle ring.
Targets cluster symmetrically on dorsal hands, feet and extensor limbs before spreading towards trunk and sometimes face.
Outer inflammation may look red, violaceous or brown while the centre appears grey, purple-black or blistered; texture and outline remain informative.
Painful oral erosions and haemorrhagic lip crust can accompany classic skin targets; ocular, genital or airway symptoms increase severity and referral need.
A cold sore or genital herpes episode often precedes targets by several days, and recurrent eruptions may follow the same sequence.
Fever, skin pain, flat atypical truncal targets, purpura, extensive mucositis and detachment after medication indicate a different emergency phenotype.
Severe oral, ocular or genital inflammation after respiratory infection with sparse vesicles or targets suggests RIME, particularly in younger people.
A medicine-related febrile illness with skin pain, flat atypical truncal targets, extensive mucositis and detachment requires emergency SJS or TEN management.
Itchy oedematous wheals migrate or disappear within a day and lack the persistent dusky three-zone centre of a true target.
One or several sharply demarcated dusky plaques recur at identical sites after the same medicine and leave conspicuous post-inflammatory pigment.
Tense or fragile blisters with characteristic mucosal patterns, histology and direct immunofluorescence lack the classic self-limited acral target sequence.
Lesions lasting over a day with purpura, residual pigment, systemic inflammation or photosensitive interface features warrant biopsy and systemic assessment.
Painful oral erosions can prevent drinking and eating, causing renal injury, weight loss and need for inpatient analgesia and fluid support.
Conjunctival inflammation can progress to epithelial defects, adhesions, dry eye and visual loss without prompt specialist examination and follow-up.
Erosive genital disease causes pain, urinary difficulty and later adhesions or stenosis, requiring respectful examination and early specialist care.
Repeated HSV-associated episodes disrupt sleep, nutrition, employment, relationships and mental wellbeing even when each eruption eventually resolves.
The word target is often applied to any annular lesion, but a classic raised three-zone target is much more discriminating for erythema multiforme.
Individual urticarial lesions usually fade within twenty-four hours, whereas erythema-multiforme targets stay fixed and evolve centrally over several days.
The triggering cold sore can heal before the immune eruption appears, so a careful preceding two-week history is more informative than current inspection alone.
Significant mucosal erythema multiforme is called EM major, but morphology, distribution and trigger still separate it from medicine-associated epidermal necrolysis.
In richly pigmented skin, concentric elevation, central vesiculation and fixed acral symmetry prevent dependence on a bright red outer ring.
Once targets emerge, treating a preceding HSV episode may not shorten that immune eruption; continuous suppression is used for frequent recurrences.
Calling every ringed lesion a target without confirming three zones, palpability and persistence.
Using erythema multiforme as a reassuring label for a painful medicine-related truncal eruption with detachment and multi-site mucositis.
Missing subtle grey, violaceous or brown central duskiness because the examination expects bright erythema on every skin tone.
Ordering HSV IgG to prove the cause of an individual episode when it mainly records common past exposure.
Prescribing repeated short antiviral courses after each target eruption instead of considering continuous suppression for frequent HSV-associated disease.
Treating severe oral pain at home without measuring hydration, urine output, ocular symptoms and the ability to swallow safely.
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Ten days after a cold sore, an otherwise well adult develops symmetrical fixed raised lesions on the backs of both hands, each with a dusky centre, pale oedematous ring and outer inflammatory rim. What is the most likely diagnosis?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
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Avoid potent products on eyelids, face or folds without supervision and do not apply into infected or deeply eroded skin; local improvement must not delay reassessment for SJS or mucosal compromise.
Adjust for renal impairment, maintain hydration and review neurotoxicity, nephrotoxicity, pregnancy and interacting nephrotoxic medicines; breakthrough lesions should trigger adherence and diagnostic review, not automatic dose escalation.