# Erythema Multiforme

> Erythema multiforme for NEET-PG Dermatology, with target lesions, HSV and Mycoplasma triggers, minor and major forms and the Stevens-Johnson distinction.

- Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/erythema-multiforme
- Exam / course: NEET-PG · Subject: Dermatology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Rook's Textbook of Dermatology; IADVL Textbook of Dermatology
- How to cite: "Erythema Multiforme", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/erythema-multiforme

## Direct answer

Erythema multiforme is an acute, self-limiting hypersensitivity reaction that produces target or iris lesions, most often after herpes simplex infection. The minor form involves the skin or a single mucosal site, while the major form involves two or more mucosal sites with systemic upset. Unlike Stevens-Johnson syndrome, classic erythema multiforme shows no sheet-like epidermal detachment, which is the key distinguishing feature.

## What you must remember

- **Target lesion:** a dusky centre surrounded by pale oedema and an outer erythematous ring, giving the iris appearance.
- **Triggers:** herpes simplex, especially recurrent HSV-associated disease, and Mycoplasma pneumoniae, with drugs such as sulphonamides and anticonvulsants.
- **Minor form:** skin lesions alone or a single mucosal site, without significant systemic features.
- **Major form:** at least two mucosal sites with systemic symptoms such as fever and malaise.
- **Recurrent disease:** HSV-associated episodes are prevented with suppressive acyclovir.
- **Histology:** interface dermatitis with keratinocyte apoptosis and basal cell damage, which overlaps with SJS.
- **Severity markers:** epidermal detachment is absent in EM, under 10 per cent of body surface area in SJS, and over 30 per cent in TEN.
- **Treatment:** supportive care and treatment of the trigger, with systemic corticosteroids reserved for severe forms where benefit is debated.

## Separating erythema multiforme from Stevens-Johnson syndrome

Erythema multiforme and Stevens-Johnson syndrome share target-like lesions but differ in mucosal load and epidermal detachment. The table sets out the contrasts examiners test most often. Each row is a contrasting pair, so the table can be recalled under exam pressure.

| Feature | Erythema multiforme | Stevens-Johnson syndrome |
| --- | --- | --- |
| Lesions | Target or iris, often acral | Atypical targets, flat dusky macules |
| Mucosal involvement | One site (minor) or two or more (major) | Severe erosions at two or more sites |
| Epidermal detachment | Absent | Present, under 10 per cent of body surface |
| Common triggers | HSV, Mycoplasma | Drugs such as sulphonamides, allopurinol, anticonvulsants |
| Systemic upset | Mild in minor, notable in major | Marked, with high fever |

Epidermal detachment is the decisive discriminator, and the percentage of body surface affected grades severity. Whenever a drug trigger is possible, withdrawing the suspected drug is the first step, regardless of the label given to the reaction. Severe cases need admission to a dermatology or burns unit, and early referral should not wait for the skin to evolve.

## Where candidates lose marks

Points of confusion here usually involve calling every target lesion erythema multiforme.

- **Trap:** calling every target lesion erythema multiforme — **Correct:** atypical targets, mucosal erosions and epidermal detachment indicate SJS, a drug reaction needing urgent review.
- **Trap:** assuming HSV-triggered erythema multiforme needs no prevention — **Correct:** recurrent HSV-associated erythema multiforme is prevented with suppressive antiviral therapy.
- **Trap:** reading erythema multiforme major as the same as SJS — **Correct:** major erythema multiforme has multiple mucosal sites but no sheet-like epidermal loss, which separates it from SJS.

## Frequently asked questions

### Which infection most often triggers erythema multiforme?

Herpes simplex virus is the commonest infectious trigger of erythema multiforme, and recurrent herpes-associated episodes are frequent. Mycoplasma pneumoniae is another important trigger, particularly in younger patients.

### How does minor erythema multiforme differ from the major form?

Minor erythema multiforme involves the skin or a single mucosal site without significant systemic upset, whereas the major form involves at least two mucosal sites with systemic symptoms. Major disease may need hospital care and close monitoring.

### What distinguishes erythema multiforme from Stevens-Johnson syndrome?

Erythema multiforme shows no sheet-like epidermal detachment, while Stevens-Johnson syndrome shows detachment of under 10 per cent of body surface area. Atypical targets, flat dusky macules and prominent mucosal erosions favour Stevens-Johnson syndrome.

### What histological pattern suggests erythema multiforme?

Erythema multiforme shows an interface dermatitis with keratinocyte apoptosis and basal cell damage, but this pattern overlaps with Stevens-Johnson syndrome. Clinical correlation is therefore essential before histology is used to label the reaction.

### How is recurrent herpes-associated erythema multiforme prevented?

Recurrent herpes-associated erythema multiforme is prevented with suppressive antiviral therapy, most often acyclovir. The regimen is individualised to how often episodes recur, and it reduces the chance of further target lesions.