Write a short note on erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis.

Definition & Spectrum

These are acute mucocutaneous reactions characterised by keratinocyte apoptosis. Erythema multiforme is now regarded as a distinct, largely infection-driven condition, whereas SJS and TEN form a single continuum, almost always drug-induced, separated by the extent of epidermal detachment.

Erythema Multiforme

• Typical target (iris) lesion — three concentric zones: a dusky or blistered centre, a pale oedematous ring, and an erythematous outer ring.
• Acral distribution — hands, feet, extensor forearms, spreading centripetally; palms and soles involved.
• EM minor: skin only. EM major: with mucosal involvement.
• Herpes simplex is the commonest trigger, often recurring with each cold sore; Mycoplasma pneumoniae is the leading cause in children.
• Management: treat the trigger; symptomatic care. Recurrent HSV-associated EM is prevented by continuous suppressive aciclovir, which is the key therapeutic point.

SJS / Ten — Causes

Over 80% are drug-induced, beginning 1–3 weeks after the drug is started:

• Anticonvulsants — carbamazepine, phenytoin, lamotrigine, phenobarbitone
• Allopurinol
• Sulphonamides — co-trimoxazole, sulfasalazine
• NSAIDs — especially oxicams
• Antibiotics — penicillins, cephalosporins, quinolones
• Nevirapine and other antiretrovirals

Also *Mycoplasma*, and in India, indigenous and unlabelled remedies. HLA-B*1502 is strongly associated with carbamazepine-induced SJS/TEN in Han Chinese and some South Asian populations, and HLA-B*5801 with allopurinol.

Clinical Features

• Prodrome of fever, malaise, sore throat and conjunctival burning for 1–3 days — often mistaken for a viral illness.
• Painful skin — pain out of proportion to visible signs is an early warning.
• Dusky red macules with atypical flat targets, becoming confluent, on the face and trunk, then spreading.
• Flaccid blisters and sheet-like epidermal detachment; Nikolsky's sign positive.
• Severe mucosal involvement in over 90% — haemorrhagic crusted lips, oral erosions preventing eating, purulent conjunctivitis with risk of symblepharon and blindness, and genital, urethral, oesophageal and respiratory epithelial involvement.
• Complications: hypovolaemia and electrolyte loss, sepsis (the commonest cause of death), hypothermia, acute kidney injury, respiratory failure from tracheobronchial epithelial sloughing, and long-term ocular scarring, dry eye, and cutaneous dyspigmentation.

Prognosis — Scorten

The SCORTEN severity score, calculated in the first 24 hours, uses seven parameters: age, presence of malignancy, heart rate, initial epidermal detachment, serum urea, serum bicarbonate and serum glucose. Mortality rises steeply with the score — approximately 5% for SJS and 30% or more for TEN.

Management

• Identify and stop the culprit drug immediately — the single measure with the clearest survival benefit; earlier withdrawal means lower mortality. Stop all non-essential drugs.
• Admit to a burns unit or intensive care. Management parallels that of extensive burns.
• Supportive care is the cornerstone: meticulous fluid and electrolyte replacement, warming, high-calorie high-protein nutrition (nasogastric if oral intake is impossible), analgesia, non-adherent dressings, avoidance of unnecessary adhesive tape, and strict asepsis. Avoid prophylactic systemic antibiotics; culture and treat infection when it occurs.
• Daily ophthalmology review from the outset to prevent ocular sequelae — the most important preventable long-term morbidity.
• Immunomodulation remains debated. Corticosteroids, intravenous immunoglobulin, ciclosporin and anti-TNF agents (etanercept) have all been used; evidence is conflicting and practice varies between centres.
• Document the drug allergy prominently, counsel the patient to avoid the drug and its class permanently, issue a card, and screen family members where an HLA association applies.