Clinical Overview

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) is a severe drug-induced reaction with systemic manifestations, characterized by the classic triad of rash, fever, and lymphadenopathy, accompanied by atypical lymphocytosis and organ involvement. DRESS typically develops 2-8 weeks after drug initiation (range 3 weeks to several months), longer than most drug reactions. Also termed "Drug-Induced Hypersensitivity Syndrome" (DIHS) in some literature, DRESS has mortality rates of 5-10% if untreated, primarily from hepatic failure or infection. Early recognition and immunosuppression are critical for improved outcomes.

Epidemiology & Risk Factors

DRESS incidence is estimated at 1 in 1,000 to 1 in 10,000 drug exposures. It accounts for 10-15% of severe cutaneous adverse reactions. Anticonvulsants are the most common triggers, accounting for 50-80% of cases: aromatic anticonvulsants (phenytoin, carbamazepine, phenobarbital) carry higher risk than non-aromatic agents (levetiracetam, valproic acid). Other frequent culprits include allopurinol (2-8% incidence in some populations), sulfonamides, NSAIDs, doxycycline, and abacavir. Cross-reactivity among anticonvulsants is common (25-30% of patients develop DRESS with a structurally similar anticonvulsant). HHV-6 and HHV-7 reactivation is implicated in pathogenesis, explaining why EBV-seropositive patients (>90% of population) have increased susceptibility. Genetic factors including HLA-A*3101 (carbamazepine), HLA-B*1502 (carbamazepine in Asian populations), and poor acetylation status increase risk.

Pathophysiology

DRESS pathogenesis involves both drug-specific CD8+ T cells and HHV-6 reactivation. Aromatic drug metabolites, particularly through cytochrome P450, generate toxic intermediates. These activate drug-specific T cells, but the disproportionate systemic response suggests additional triggers. HHV-6 reactivation (detected in 50-80% of DRESS cases) may act as a co-trigger, amplifying immune activation. Abnormal T regulatory cell (Treg) function is a key mechanism—patients show reduced Treg numbers and decreased IL-10 production, allowing unchecked T cell proliferation. This results in massive lymphoid hyperplasia (generalized lymphadenopathy, hepatomegaly, splenomegaly). Eosinophilia arises from Th2 cytokine production (IL-5, IL-13), particularly when HHV-6 reactivation is present.

Clinical Presentation & Classification

DRESS typically presents with fever (60-80% of cases), often 38-40°C, accompanied by facial edema (30-50% of cases), which is highly characteristic. Rash appears within days of fever onset: polymorphic (morbilliform most common, but can be scarlatiniform, urticarial, or even purpuric), typically involving face and trunk with spread to extremities. Generalized lymphadenopathy is nearly universal (>85% of cases), particularly cervical, axillary, and inguinal nodes. Liver involvement is common: mild hepatomegaly in 30-40%, elevated transaminases (ALT/AST >100 IU/L) in 40-80%, and severe hepatitis with jaundice in 5-15% of cases. Kidney involvement is less common (10-15%), manifested as acute kidney injury or tubulointerstitial nephritis. Cardiac involvement (myocarditis, arrhythmias) occurs in 5-10%. Respiratory involvement (pneumonitis, pulmonary edema) can develop.

RegiSCAR scoring system (developed to standardize diagnosis): Score ≥3 indicates probable case; ≥4 indicates definite case. Factors include fever, atypical lymphocytes, hepatomegaly, eosinophilia, and lymphadenopathy.

Diagnosis & Workup

Diagnosis requires combination of clinical features and laboratory findings (no single pathognomonic test). Skin biopsy, while not specific, shows inflammatory pattern consistent with drug reaction (interface dermatitis, sometimes with atypical lymphocytes resembling lymphoma).

Essential workup includes:

  • Complete metabolic panel and liver function tests—elevated transaminases (typically ALT/AST 3-10 times normal), hyperbilirubinemia indicates severe hepatitis
  • Complete blood count—atypical lymphocytosis (activated T lymphocytes) in 50-70%, eosinophilia (>1,500/μL in 40-90%), mild leukocytosis
  • Peripheral blood smear—atypical lymphocytes ("Atypical Lymphocyte Syndrome" appearance)
  • Blood cultures and serologies—exclude infectious causes (EBV, CMV); HHV-6 PCR if available
  • Imaging: chest X-ray (pneumonitis?), abdominal ultrasound or CT (hepatomegaly, splenomegaly?)
  • Lymph node biopsy (only if diagnosis unclear or concern for malignancy)—shows reactive hyperplasia, not lymphoma

Distinguish DRESS from mononucleosis, EBV infection, lymphoma, and serum sickness. The temporal relationship to drug initiation and resolution with drug discontinuation support DRESS diagnosis.

Treatment Algorithm

Immediate: Discontinue causative drug. Avoid rechallenge—it will cause recurrence in nearly 100% of cases.

First-line: Systemic corticosteroids. These are essential and highly effective. Typical regimen: methylprednisolone 1-2 mg/kg/day IV or prednisone 1-2 mg/kg/day (50-100 mg daily), then slow taper over 8-12 weeks. Most patients show dramatic improvement (fever resolves in 1-2 weeks, rash in 2-4 weeks, organ dysfunction in 2-4 weeks). Rapid discontinuation or insufficient doses lead to rebound flares requiring re-escalation.

Supportive care: Monitor liver function weekly initially. Continue hepatic support (avoid hepatotoxic drugs, alcohol; ensure adequate nutrition). Address complications: diuretics for edema, antibiotics only if bacterial superinfection documented.

Second-line agents (for severe cases or steroid resistance):

  • Intravenous immunoglobulin (IVIG): 2 g/kg over 3-5 days, particularly for fulminant hepatitis
  • Cyclosporine: 3-5 mg/kg/day as adjunct to steroids in severe, refractory cases
  • Mycophenolate mofetil or azathioprine: for steroid-sparing effect
  • HHV-6 reactivation: Some authorities recommend ganciclovir or foscarnet if HHV-6 PCR is positive and severe disease, though evidence is limited

Prognosis & Complications

Mortality ranges from 5-10% with modern treatment, primarily from hepatic failure or opportunistic infection. Fulminant hepatitis (INR >2, encephalopathy) carries higher mortality (20-50%). With prompt recognition and corticosteroid initiation, most patients recover fully. Long-term sequelae are uncommon: some patients develop organ-specific autoimmune diseases (particularly hypothyroidism) in 10-15% of cases. Reactivation of HHV-6 can occur even after recovery, rarely leading to recurrent symptoms.

When to See a Dermatologist

Seek urgent evaluation if you develop fever, rash, facial edema, and generalized lymphadenopathy within weeks of starting a new medication, particularly an anticonvulsant or allopurinol. This is a medical emergency requiring hospitalization. Early dermatology consultation combined with hepatology input is critical for rapid diagnosis and management.

Frequently Asked Questions

Why does DRESS take so long to develop after starting the drug?

Unlike immediate allergic reactions (driven by pre-formed mast cell mediators), DRESS requires time for your immune system to recognize the drug metabolite, generate drug-specific T cells, and produce sufficient T cell responses. This takes 2-8 weeks or longer. HHV-6 reactivation, which develops over time, likely amplifies the response.

What is the difference between DRESS and mononucleosis?

Both cause fever, rash, and atypical lymphocytes. Key differences: DRESS has temporal relationship to drug initiation; mononucleosis is EBV-driven. DRESS shows elevated liver enzymes (ALT/AST) more dramatically than mono. Mono typically causes pharyngitis (absent in DRESS). EBV serology helps distinguish: mono is associated with acute EBV infection; DRESS has remote EBV infection (you're already immune). Finally, DRESS worsens without stopping the causative drug, while mono resolves spontaneously.

Is DRESS the same as Stevens-Johnson Syndrome?

No. Both are severe drug reactions, but DRESS develops more slowly (weeks), while SJS develops over days. DRESS features prominent systemic symptoms (fever, lymphadenopathy, organ involvement, atypical lymphocytes). SJS features rapidly progressive mucocutaneous lesions with blistering/detachment and potential for epidermal necrosis. DRESS responds dramatically to steroids; SJS is managed with supportive care and immunosuppression but has different treatment priorities.

Will I have lifelong problems from DRESS?

Most patients recover fully with appropriate treatment. Long-term complications are uncommon but include autoimmune thyroiditis (10-15% of survivors). Some patients report persistent fatigue or mild cognitive symptoms. HHV-6 remains latent in your system (like any herpesvirus) but typically does not reactivate. The causative drug should be avoided forever due to nearly universal recurrence risk.

References

  1. Kardaun SH, et al. Variability in the clinical pattern of cutaneous side-effects of drugs with systemic symptoms: Does a DRESS syndrome really exist? Br J Dermatol. 2007;156(3):609-611.
  2. Bouvresse S, et al. Severe systemic and cutaneous manifestations of drug hypersensitivity syndrome. Arch Dermatol. 2012;148(2):207-216.
  3. Peyrière H, et al. Correlations between clinical features and biologic abnormalities in 48 cases of DRESS syndrome. Arch Dermatol. 2012;148(6):675-684.
  4. Miyahara H, et al. HHV-6 reactivation in drug-induced hypersensitivity syndrome (DIHS)/DRESS syndrome. J Dermatol. 2019;46(3):239-245.
  5. Ushigome Y, et al. HHV-6 reactivation as a prognostic marker in DRESS. J Am Acad Dermatol. 2015;73(5):733-740.
  6. Ushigome Y, et al. Severe systemic manifestations in drug reaction with eosinophilia and systemic symptoms. J Dermatol. 2015;42(3):276-282.
  7. Cho YT, et al. Human herpesvirus 6 reactivation in drug reaction with eosinophilia and systemic symptoms (DRESS): a marker of severe disease. Br J Dermatol. 2013;168(6):1298-1304.
  8. Lerch M, et al. Drug-induced hypersensitivity syndrome. Clin Exp Allergy. 2013;43(12):1409-1417.