Dermatological emergencies in the SCE: SJS/TEN, DRESS, erythroderma and necrotising fasciitis

2026-08-02

A high-yield guide to dermatological emergencies for the UK Dermatology SCE: SJS/TEN, DRESS, erythroderma and necrotising fasciitis, with the ABCDE priorities, SCORTEN variables, RegiSCAR criteria and the traps examiners love.

Illustration of emergency monitoring beside a patient with widespread inflamed skin

Dermatological emergencies are a favourite of the Dermatology SCE because they test exactly what a safe registrar does on a real referral: recognise a dangerous pattern quickly, protect the patient with supportive care, stop whatever is driving the illness, and escalate early. They are uncommon enough that many candidates revise them lightly, which is precisely why a few clean questions can separate a pass from a fail. This guide covers four scenarios the examiners return to again and again: Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), erythroderma, and necrotising fasciitis. For each one we focus on the stable, examinable facts rather than shifting numbers, and we flag the traps that catch people out.

Before any specific diagnosis, remember the principle that underlies every emergency answer: assess and resuscitate first, diagnose second. A structured ABCDE approach comes before pattern recognition in the acutely unwell patient. If a stem describes a shocked, hypoxic or peri-arrest patient, the correct first step is almost never a skin biopsy or a specialist referral; it is airway, breathing, circulation, and calling for help. Keep that ordering in mind, because SCE questions often bury the emergency step among plausible but lower-priority distractors.

The shared emergency mindset: ABCDE, stop the culprit, escalate early

Three actions run through almost every dermatological emergency answer, and they generalise across the whole topic. First, immediate supportive care using an ABCDE framework: secure a threatened airway, give oxygen and fluid resuscitation as needed, manage pain, correct electrolytes, and keep the patient warm. Extensive skin loss behaves like a burn, so fluid balance, temperature regulation and infection control all matter. Second, stop the culprit: in drug-induced reactions the single most important therapeutic step is to identify and withdraw the offending medication, and any recently started drug within the plausible latency window is a suspect. Third, escalate early: these patients need senior dermatology input, and many need critical care, burns or plastic surgery, with ophthalmology involved for mucosal disease.

SJS/TEN: mucosae, detachment and SCORTEN

SJS and TEN sit on a single spectrum of mucocutaneous blistering with epidermal detachment, classified by the body surface area (BSA) of detached or detachable skin. Stevens-Johnson syndrome involves less than 10 percent BSA, toxic epidermal necrolysis more than 30 percent BSA, and the overlap category covers 10 to 30 percent. Memorise those cut-offs precisely, because a question will often give a percentage and expect the label. The classic prodrome is fever and malaise, followed by painful skin, atypical target lesions and, crucially, involvement of two or more mucosal sites: eyes, mouth and genitals. Skin pain out of proportion to the visible rash, a positive Nikolsky sign and tender erythema are all red flags for early detachment.

The culprit is a drug in the great majority of cases, and the high-yield offenders are allopurinol, aromatic anticonvulsants such as carbamazepine, lamotrigine and phenytoin, sulfonamide antibiotics, nevirapine and the oxicam NSAIDs. Onset is typically within one to three weeks of starting the drug. Certain HLA associations are examinable, most famously HLA-B*15:02 with carbamazepine-induced SJS/TEN in people of Han Chinese and some other South-East Asian ancestries, and HLA-B*58:01 with allopurinol reactions.

Management follows the emergency mindset exactly: stop the suspected drug immediately, resuscitate along ABCDE lines, and manage these patients in an appropriate high-dependency, burns or intensive care setting with dermatology and ophthalmology involved early. Meticulous supportive care is the backbone of treatment: fluid and electrolyte balance, temperature control, analgesia, nutritional support, sterile wound care and prompt treatment of infection. Systemic immunomodulatory therapies are used by specialists, but the evidence base is limited and there is no single universally agreed first-line agent, so in an exam the safe emphasis is supportive care, drug withdrawal and early escalation rather than committing to one immunomodulator.

For prognosis, know SCORTEN as a validated severity-of-illness score. You are far more likely to be asked which variables it uses than to be asked a precise mortality percentage, so learn the seven parameters and avoid quoting exact figures you cannot verify.

Age of 40 years or over.
Malignancy present.
Heart rate of 120 beats per minute or more.
Initial epidermal detachment of more than 10 percent body surface area.
Serum urea greater than 10 mmol/L.
Serum bicarbonate less than 20 mmol/L.
Serum glucose greater than 14 mmol/L.

DRESS: the slow-burn reaction with organ involvement

DRESS, also called drug-induced hypersensitivity syndrome, is the great mimic and a reliable SCE topic because its features are systemic rather than purely cutaneous. The two facts that anchor every DRESS question are its latency and its organ involvement. The latency is long: the reaction typically begins two to eight weeks after starting the culprit drug, far later than most drug rashes, and this is a classic discriminator in a stem. It then tends to evolve and can persist or relapse even after the drug is stopped, unlike a simple morbilliform eruption that settles quickly.

The clinical picture combines a widespread rash, often with facial oedema, with fever, lymphadenopathy and internal organ involvement. The blood picture classically shows eosinophilia and sometimes atypical lymphocytes. The liver is the most commonly affected internal organ, but the kidneys, lungs, heart and others can be involved, so DRESS is a multisystem diagnosis rather than a skin diagnosis. Reactivation of herpesviruses, particularly HHV-6, is a recognised association examiners occasionally test. Typical culprits overlap with SJS/TEN and include aromatic anticonvulsants, allopurinol, sulfonamides, vancomycin and minocycline.

The RegiSCAR criteria are the recognised framework used to grade how likely a case is to be DRESS, drawing together exactly the features above: fever, lymphadenopathy, eosinophilia, atypical lymphocytes, skin involvement, internal organ involvement, resolution taking more than 15 days, and exclusion of other causes. You do not need to reproduce the full weighted scoring, but you should recognise RegiSCAR as the tool and know the domains it assesses. Management is again to stop the culprit drug and give supportive care, with systemic corticosteroids commonly used for significant organ involvement under specialist guidance, plus monitoring for delayed complications such as thyroid dysfunction weeks to months later.

Erythroderma: when more than 90 percent of the skin is inflamed

Erythroderma, also called exfoliative dermatitis, is defined as erythema affecting more than 90 percent of the body surface area, usually with scaling. It is a clinical state rather than a single disease, and its danger comes from loss of the skin barrier over almost the entire body. The commonest causes to have ready are pre-existing dermatoses that have flared, especially psoriasis and eczema, drug reactions, and underlying malignancy including cutaneous T-cell lymphoma such as Sezary syndrome. A useful exam habit is to group the causes as dermatitis, drugs, dermatoses and malignancy, and to remember that a proportion of cases remain idiopathic.

The complications flow logically from a failed skin barrier and are the examinable core. Widespread vasodilatation causes heat and fluid loss, leading to hypothermia, dehydration and high-output cardiac failure in vulnerable patients. Protein loss from scaling contributes to hypoalbuminaemia, the broken barrier predisposes to secondary infection and even sepsis, and electrolyte disturbance is common. Management is supportive and mirrors the emergency mindset: admit, keep the patient warm, correct fluid and electrolyte imbalance, treat infection, apply generous emollients and bland topical care, stop any potential culprit drug, and work up the underlying cause while dermatology leads treatment of the trigger.

Necrotising fasciitis: pain out of proportion and the knife, not the calculator

Necrotising fasciitis is a surgical emergency and the sharpest exam trap in this topic, because the early skin signs can look deceptively unimpressive. The classic teaching, and the answer the examiners want, is pain out of proportion to the visible findings. Early on the overlying skin may show only mild erythema while the patient reports severe, rapidly worsening pain, systemic toxicity and features of sepsis. As it advances you may see dusky or bluish discolouration, bullae, skin anaesthesia from destroyed cutaneous nerves, crepitus, and rapid spread with a poorly demarcated edge. Risk factors include diabetes, immunosuppression, peripheral vascular disease and injecting drug use.

The management principle is unambiguous and high-yield: immediate resuscitation and urgent surgical exploration and debridement, alongside broad-spectrum intravenous antibiotics and treatment of sepsis. Surgery is both diagnostic and therapeutic and must not be delayed for imaging or laboratory scores. Treat sepsis in parallel using a recognised framework such as the NICE sepsis guidance. In an exam, if the stem describes pain out of proportion, systemic toxicity and rapidly progressive signs, the correct next step is urgent surgical review, not further investigation.

The LRINEC score deserves specific attention because it is a classic trap. LRINEC combines routine blood parameters such as C-reactive protein, white cell count, haemoglobin, sodium, creatinine and glucose to estimate the risk of necrotising fasciitis. It can raise suspicion, but a low LRINEC score does not exclude the diagnosis. Necrotising fasciitis remains a clinical diagnosis, and a reassuring score must never delay surgery in a patient with convincing clinical features. If a question tempts you to send the patient for more tests because the LRINEC is low, that is the wrong answer.

How to revise this for the SCE

Build a single comparison table with the four emergencies down the side and a few columns across the top: defining feature, typical latency or trigger, the standout complication, and the one management priority. For SJS/TEN capture the BSA cut-offs and the SCORTEN variables; for DRESS the two-to-eight-week latency, eosinophilia and liver involvement, and RegiSCAR as the framework; for erythroderma the greater than 90 percent definition and the hypothermia and cardiac failure complications; and for necrotising fasciitis pain out of proportion and immediate surgery. Then drill the table with questions rather than re-reading it, because the SCE rewards fast recognition under time pressure. These emergencies overlap heavily with the wider drug reaction syllabus, so revise them alongside our guide to cutaneous drug reactions in the SCE, and sharpen your technique with our guide on how to approach SBA questions in dermatology.

Finally, keep the ordering discipline. In any emergency stem, resuscitate before you investigate and investigate before you commit to a specific treatment. Stop the culprit drug, protect the barrier, treat sepsis and escalate early. Do that consistently and the emergencies section becomes one of the most predictable and rewarding parts of the whole exam.

Sources & further reading

For educational use only. Check current official guidance.

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