01OverviewDefinition, clinical context and the essential points that orientate the chapter.
DRESS usually evolves later than a simple exanthem. Fever and an extensive infiltrated eruption are accompanied by facial oedema, lymphadenopathy and blood abnormalities such as eosinophilia or atypical lymphocytes. Internal injury may be initially silent, and skin extent does not reliably predict myocarditis or hepatitis severity.
Stop the most plausible culprit promptly, but avoid creating an unexamined list of every medicine as equally causal. Record start, stop and dose dates, known latency, organ pattern and alternatives. Stable patients still need serial monitoring because eosinophilia and organ injury can peak after withdrawal. Severe hepatitis, nephritis, pneumonitis or myocarditis needs multidisciplinary inpatient care.
Clinical decisions in DRESS syndrome depend on trajectory and consequence. Re-examine evolving skin, repeat focused systemic assessment when the patient changes, and reconcile every result with morphology and timing; a normal early test cannot neutralise worsening pain, mucosal injury or organ dysfunction.
Key points
- Suspect DRESS when a widespread drug eruption appears two to eight weeks after exposure with fever, facial oedema, nodes, eosinophilia or organ injury.
- Examine for infiltrated oedema, especially face and ears, but recognise active erythema may appear violaceous, grey or brown in deeply pigmented skin.
- List every medicine taken during the preceding two months, including antibiotics already completed and dose escalation of long-term treatments.
- Use a validated framework such as RegiSCAR to structure probability, while treating urgent organ disease before the score is complete.
- Check FBC with differential, blood film, liver, renal and urinalysis, then add cardiac, pulmonary or pancreatic tests from symptoms and repeat serially.
- Systemic corticosteroid decisions and taper are specialist-led because organ severity varies and relapse can follow rapid reduction.
- DRESS syndrome must be assessed by lesion duration, onset, distribution, symptoms, mucosal findings, systemic physiology and the full medicine timeline rather than by colour alone.
- For DRESS syndrome, document the working diagnosis, excluded emergencies, uncertain culprit or trigger, treatment response and the exact safety-net given.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
High-risk culprit medicines
Aromatic antiseizure medicines, allopurinol, sulfonamides, vancomycin and several other drugs are recognised triggers, with risk modified by dose, renal function and genotype.
Delayed immune hypersensitivity
Symptoms typically begin two to eight weeks after first exposure, so recently discontinued medicines and hospital-administered courses must remain on the timeline.
Viral reactivation interplay
Herpesvirus reactivation often accompanies the syndrome and may amplify immune dysfunction, but it is neither required nor sufficient for diagnosis.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Drug-reactive lymphocytes
Culprit metabolites or immune interactions activate T cells that infiltrate skin and organs and release cytokines recruiting eosinophils.
- 2Multiorgan inflammation
Liver is affected most often, while kidney, lung, heart, pancreas and nervous system injury can arise asynchronously and worsen after withdrawal.
- 3Prolonged immune activation
Slow drug clearance, immune amplification and viral reactivation contribute to relapses during recovery or overly rapid corticosteroid reduction.
- 4Late immune dysregulation
Survivors have increased risk of subsequent autoimmune thyroid, glucose and other disorders, requiring follow-up beyond visible rash resolution.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
A widespread infiltrated rash with fever beginning weeks after a high-risk medicine is the core temporal signal.
Prominent swelling, often accentuated around eyelids and ears, is a useful clue but is not universal.
Eosinophilia, atypical lymphocytes, leukocytosis or cytopenias support systemic drug hypersensitivity and should be trended.
Jaundice, renal change, breathlessness, chest pain, hypotension or neurological symptoms can indicate life-threatening visceral disease.
New lesions, fever or biochemical injury may continue after the drug is withdrawn and relapse during recovery.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Full medicine chronologyFirst step - Why
- Rank plausible culprits using exposure dates, known latency, dose and organ phenotype.
- Interpretation and limitations
- Include medicines stopped several weeks earlier; attribution scores support judgement but cannot replace careful clinical review.
- 02
FBC, differential and blood film - Why
- Detect eosinophilia, atypical lymphocytes and cytopenia for diagnosis and severity.
- Interpretation and limitations
- Counts can be normal early and peak later, while corticosteroids alter them; repeat results rather than relying on one sample.
- 03
Liver, renal, urinalysis and coagulation - Why
- Find common silent visceral injury and hepatic synthetic failure.
- Interpretation and limitations
- Trend ALT, bilirubin, creatinine, urine blood and protein; rising INR or jaundice signals urgent specialist escalation.
- 04
ECG, troponin and cardiac imaging when indicated - Why
- Detect myocarditis in patients with chest symptoms, tachycardia or haemodynamic change.
- Interpretation and limitations
- DRESS myocarditis can be rapidly fatal, and a normal initial ECG alone does not exclude evolving injury.
- 05
Biopsy and targeted infection testing - Why
- Support pattern classification and evaluate important mimics.
- Interpretation and limitations
- Histology is not pathognomonic and herpesvirus results require specialist interpretation; do not postpone withdrawal for either.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Morbilliform drug eruption
An uncomplicated exanthem lacks prominent facial oedema, sustained fever, eosinophilia and internal-organ dysfunction and usually settles quickly after withdrawal.
AGEP
Acute generalised pustulosis usually has a much shorter drug latency, neutrophilia and numerous sterile non-follicular pustules followed by rapid desquamation.
SJS or TEN
Skin pain, mucosal erosion, dusky atypical targets and epidermal detachment support necrolysis rather than the infiltrated oedematous exanthem of DRESS.
Infection or malignancy
Sepsis, viral infection, lymphoma and hypereosinophilic disease can reproduce fever, nodes, rash and organ abnormalities and may coexist with medicine exposure.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Probable DRESSWithdraw and map organ involvementFirst stepA delayed drug eruption includes fever, facial oedema, blood abnormalities or any internal-organ signal.+
- 1Stop plausible non-essential culprits, admit when systemic involvement is significant and obtain dermatology plus acute-medical review.
- 2Apply a structured diagnostic framework and assess blood, liver, kidney, urine and symptom-directed cardiac, lung or pancreatic involvement.
- 3Record baseline physiology and serial laboratory values because deterioration can occur after the medicine is withdrawn.
02Severe organ diseaseCoordinate specialist immunosuppression and supportHepatitis, nephritis, pneumonitis, myocarditis, encephalitis or haemodynamic instability is present.+
- 1Involve the relevant organ and critical-care teams immediately, deliver organ support and exclude infection that would alter immunosuppression.
- 2AlternativeUse systemic corticosteroid or alternative immunomodulatory treatment through an experienced specialist plan tailored to the threatened organ.
- 3Taper only against sustained clinical and biochemical improvement, watching for relapse rather than following a short fixed course.
03Recovery phasePrevent relapse and late harmSkin and organ abnormalities are improving after culprit withdrawal and acute treatment.+
- 1Continue serial FBC and affected-organ monitoring until stable resolution, extending review when injury, eosinophilia or immunosuppression persists.
- 2Provide a precise allergy record, written avoidance advice and specialist review of potential cross-reactive medicines.
- 3Check symptoms and thyroid or glucose testing over subsequent months when clinically indicated because delayed autoimmune sequelae occur.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Fulminant organ failure
Hepatitis can progress to coagulopathy, nephritis to renal failure and myocarditis to arrhythmia or shock despite withdrawal of the drug.
Delayed relapse
Rash, eosinophilia or organ injury may recur weeks later, particularly with infection, a new drug or rapid immunosuppression reduction.
Secondary autoimmunity
Autoimmune thyroiditis, type 1 diabetes and other immune disorders can emerge months after apparent recovery and require symptom-led surveillance.
Cross-reactive re-exposure
Poorly specified allergy records can lead to repeat exposure or use of structurally related high-risk medicines with a faster severe response.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Trend eosinophils, liver, kidney, urine and every initially affected organ until recovery is sustained after DRESS.
- During corticosteroid treatment, monitor infection, glucose, blood pressure, bone protection and relapse with each dose reduction.
- Arrange longer-term review for fatigue, thyroid symptoms, polyuria, weight change or recurrence after a new medicine.
- At every review of DRESS syndrome, record lesion evolution, new mucosal or systemic features, medicine changes, treatment adherence and adverse effects.
- Give a named route for urgent reassessment if breathing, circulation, fever, skin pain, blistering, facial swelling, reduced urine output or other organ symptoms develop during DRESS syndrome.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Stopping the drug is not the endpoint
Immune and organ injury can continue for weeks after exposure ends, so discharge requires an explicit biochemical follow-up owner.
The face is informative
Periorbital and auricular oedema helps distinguish DRESS from a flat uncomplicated morbilliform eruption.
Heart disease may be quiet
Unexplained tachycardia, chest symptoms or hypotension should prompt myocarditis assessment even when skin is improving.
Eosinophilia can arrive late
A normal initial differential does not exclude DRESS when timing, fever and organ injury remain convincing.
New drugs can provoke relapse
During active recovery, introduce only necessary medicines with careful documentation because immune activation remains unstable.
11Common pitfallsFrequent interpretation and management errors.
- 01
Excluding DRESS because the culprit course finished before the rash began.
- 02
Discharging after skin improvement without repeat liver, renal and haematological testing.
- 03
Assuming rash severity predicts whether myocarditis or hepatitis is present.
- 04
Giving a rapid corticosteroid taper without monitoring for recurrent fever and organ injury.
- 05
Entering every simultaneous medicine as a confirmed allergy without ranking likelihood and considering future treatment needs.