2025 PACUPrep BCCCP Preparatory Course Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis Foundational Principles: Epidemiology, Pathophysiology & Risk Factors
SJS/TEN: Epidemiology, Pathophysiology & Risk Factors

Foundational Principles: Epidemiology, Pathophysiology & Risk Factors of SJS/TEN

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Lesson Objective

Summarize incidence and mortality of Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), explain T-cell–mediated keratinocyte apoptosis, and analyze clinical risk factors including chronic disease and social determinants.

1. Epidemiology & Demographics

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare but life-threatening severe mucocutaneous adverse reactions. Their incidence is low, but mortality is directly correlated with the extent of epidermal detachment, underscoring the need for rapid diagnosis and specialized care.

1.1 Incidence & Mortality

Globally, SJS/TEN affects between 1 and 9 individuals per million each year. Mortality rises sharply as the affected body surface area (BSA) increases.

SJS/TEN Classification and Associated Mortality
Classification Body Surface Area (BSA) Detached Approximate Mortality Rate
SJS <10% 5–10%
SJS/TEN Overlap 10–30% 10–20%
TEN >30% 25–40%

1.2 Geographic & Genetic Factors

Incidence patterns reveal strong pharmacogenetic associations, particularly in certain ethnic groups. For instance, carbamazepine-induced SJS/TEN is more common in Southeast Asian populations due to the higher prevalence of the HLA-B15:02 allele. Similarly, allopurinol-related reactions are more frequent in Han Chinese and Korean populations carrying the HLA-B58:01 allele. This has led to successful preventative screening programs in some regions; pre-prescription HLA-B*15:02 screening in Taiwan reduced the incidence of carbamazepine-induced SJS/TEN by over 90%.

Pearl Icon A shield with an exclamation mark, indicating a clinical pearl. Clinical Pearl: Early Referral and Genetic Consideration +

Survival in SJS/TEN is significantly improved with early transfer to a specialized burn unit or intensive care unit (ICU). When prescribing high-risk medications like carbamazepine or allopurinol, always consider the patient’s genetic background and the potential utility of pharmacogenomic screening in at-risk populations.

2. Drug Triggers & Latency Periods

Medications are the primary cause of SJS/TEN, implicated in over 70% of cases. The reaction is typically a delayed, type IVc hypersensitivity response, with a characteristic latency period between drug initiation and symptom onset.

2.1 High-Risk Medications

A few drug classes account for the majority of cases. The risk is highest during the first 8 weeks of therapy.

Common High-Risk Drugs for SJS/TEN
Drug/Class Approximate Risk Typical Latency Period
Allopurinol 0.1–0.4% in new users 4–8 weeks
Carbamazepine >1 in 5,000 new users 2–4 weeks
Lamotrigine ~1 in 1,000 adults 2–8 weeks
Sulfonamides (e.g., TMP-SMX) High, variable 1–3 weeks
Oxicam NSAIDs (e.g., Piroxicam) Moderate 1–3 weeks
Immune Checkpoint Inhibitors Low but reported Variable (weeks to months)

2.2 Latency and Causality Assessment

The typical onset of symptoms is 4 to 28 days after starting a new high-risk medication. A shorter latency of less than 7 days may suggest prior sensitization or re-challenge. In cases of polypharmacy, determining the culprit drug can be challenging. The ALDEN (Algorithm of Drug Causality for Epidermal Necrolysis) is a validated tool used to retrospectively assess the probability of each suspected drug being the cause.

Tip Icon A lightbulb, indicating a clinical tip. Clinical Tip: The Drug Timeline is Critical +

When SJS/TEN is suspected, obtain a meticulous and precise timeline of all medications started within the preceding 8 weeks. This includes over-the-counter (OTC) drugs, herbal supplements, and recent antibiotic courses. Rank suspected agents based on their known risk (notoriety), the timing of their initiation (latency), and any available patient-specific data, such as genotype.

3. Immunologic Pathophysiology

SJS/TEN is fundamentally a T-cell-mediated process where the body’s immune system mistakenly attacks its own skin and mucosal cells, leading to widespread cell death (apoptosis) and detachment.

Pathophysiology of SJS/TEN A flowchart showing the immune cascade in SJS/TEN. It starts with a drug binding to an HLA molecule on a keratinocyte, which activates a CD8+ T-cell. The T-cell then releases granulysin and other mediators, causing widespread keratinocyte apoptosis. 1. Drug/Metabolite Binds to HLA Class I on Keratinocyte 2. CD8+ Cytotoxic T-Cell Recognizes Drug-HLA Complex & Activates 3. Release of Cytotoxic Mediators • Granulysin (Key Mediator) • Perforin / Granzyme B • Fas Ligand (FasL) 4. Widespread Keratinocyte Apoptosis & Necrolysis
Figure 1: The Immunologic Cascade of SJS/TEN. The reaction is initiated by the presentation of a drug by specific HLA molecules, leading to the activation of cytotoxic T-cells. These cells release granulysin, the primary effector molecule, which induces massive apoptosis of keratinocytes, resulting in epidermal detachment.

3.1 Key Mediators

  • Type IVc Hypersensitivity: This classification denotes a T-cell-mediated reaction where cytotoxic CD8+ T-cells are the primary drivers of tissue damage.
  • Granulysin: This is considered the principal cytotoxic protein responsible for keratinocyte death in SJS/TEN. Its concentration in blister fluid directly correlates with disease severity.
  • Other Molecules: Perforin/granzyme B pathways and the engagement of the Fas receptor on keratinocytes by Fas Ligand (FasL) on T-cells also contribute significantly to the apoptotic cascade. Interleukin-15 (IL-15), released by stressed keratinocytes, further amplifies the cytotoxic immune response.

4. Genetic & Host Susceptibility

A patient’s genetic makeup, specifically their Human Leukocyte Antigen (HLA) type, is the single most important risk factor for developing SJS/TEN in response to certain drugs. These associations are so strong that they form the basis for preventative screening.

Key Pharmacogenetic Associations in SJS/TEN
HLA Allele Associated Drug High-Prevalence Populations
HLA-B*15:02 Carbamazepine, Phenytoin Han Chinese, Southeast Asians (e.g., Thai, Malaysian)
HLA-B*58:01 Allopurinol Han Chinese, Korean, Thai, Europeans
HLA-A*31:01 Carbamazepine Europeans, Japanese, Koreans

5. Impact of Chronic Comorbidities

Certain underlying chronic diseases, particularly those involving immune dysregulation, dramatically increase the risk of SJS/TEN and are associated with poorer outcomes.

5.1 HIV/AIDS

Patients with HIV infection have a risk of developing SJS/TEN that is up to 1,000 times higher than that of the general population. The exact reasons are multifactorial but are thought to involve chronic immune activation, altered drug metabolism pathways, and a higher burden of coinfections that may act as co-triggers.

Controversy Icon A chat bubble with a question mark, indicating a point of controversy or debate. Knowledge Gap: Autoimmune Disease & Biologics +

While systemic lupus erythematosus (SLE) is a known risk factor, specific risk data for many other autoimmune disorders and the impact of biologic therapies are sparse. The interplay between underlying disease activity, immunosuppressive medications, and SJS/TEN risk is a critical area for future research. Clinicians should maintain a high index of suspicion in these complex patient populations.

6. Social Determinants of Health

Socioeconomic factors, access to care, and health literacy can significantly impact the timely diagnosis and management of SJS/TEN, thereby influencing patient outcomes.

6.1 Access and System-Level Barriers

In many settings, delays in seeking medical care are common due to cost, geographic distance to facilities, or lack of transportation. Furthermore, the absence of established referral pathways to specialized burn centers or ICUs can lead to prolonged exposure to the culprit drug and a delay in initiating critical supportive care, worsening morbidity and mortality.

6.2 Health Literacy and Cultural Factors

Low health literacy can prevent patients from recognizing early warning signs (e.g., fever, mucosal pain, spreading rash) and linking them to a new medication. This can delay the crucial first step: cessation of the offending drug. In some cultures, initial reliance on traditional remedies can further complicate the identification of the trigger and delay presentation to a medical facility.

Pearl Icon A shield with an exclamation mark, indicating a clinical pearl. Pearl: Empower Patients with Simple Checklists +

Patient education is a powerful preventative tool. When starting a high-risk medication, empower patients and community healthcare providers with a simple recognition checklist: Fever + Painful Mouth/Eye Sores + New Spreading Rash. This simple triad should prompt immediate cessation of the new drug and urgent medical consultation.

7. Clinical Implications & Research Directions

Early and accurate risk stratification is crucial for predicting prognosis and guiding the level of care. Ongoing research is focused on identifying early biomarkers and novel therapeutic targets to halt disease progression.

7.1 Risk Stratification Scores

Validated scoring systems help predict mortality at the time of admission. SCORTEN is the most widely used, while ABCD-10 offers an alternative with enhanced focus on renal risk factors.

Prognostic Scoring Systems in SJS/TEN
Scoring System Key Criteria (1 point each)
SCORTEN Age ≥40; Malignancy; Heart rate ≥120; BSA detached >10%; Urea >28 mg/dL; Glucose >252 mg/dL; Bicarbonate <20 mmol/L
ABCD-10 Age ≥50; Bicarbonate <20 mmol/L; Active Cancer; Dialysis (chronic); BSA detached >10%

7.2 Biomarkers and Future Therapies

The future of SJS/TEN management lies in earlier diagnosis and targeted intervention. Blister-fluid granulysin and serum IL-15 are promising biomarkers that correlate with severity and may one day serve as rapid diagnostic tools. Therapeutically, research is exploring agents that can modify the immune response, such as RIP kinase inhibitors (to block necroptosis) and other T-cell modulating therapies, to stop the destructive cascade before significant tissue damage occurs.

References

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  2. Chang HC, Wang TJ, Lin MH, Chen TJ. A review of the systemic treatment of Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis. Biomedicines. 2022;10(9):2105.
  3. Chung WH, Hung SI, Yang JY, et al. Granulysin is a key mediator for disseminated keratinocyte death in Stevens-Johnson syndrome and toxic epidermal necrolysis. Nat Med. 2008;14(12):1343–1350.
  4. Frantz R, Huang S, Are A, Motaparthi K. Stevens-Johnson syndrome and toxic epidermal necrolysis: A review of diagnosis and management. Medicina (Kaunas). 2021;57(9):895.
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  6. Heuer R, Paulmann M, Annecke T, et al. S3 guideline: Diagnosis and treatment of epidermal necrolysis—Part 1. J Dtsch Dermatol Ges. 2024;22:1448–1466.
  7. Mockenhaupt M, Messenheimer J, Tennis P, Schlingmann J. Risk of Stevens-Johnson syndrome and toxic epidermal necrolysis in new users of antiepileptics. Neurology. 2005;64(7):1134–1138.
  8. Noe MH, Rosenbach M, Hubbard RA, et al. Development and validation of ABCD-10 for in-hospital mortality in SJS/TEN. JAMA Dermatol. 2019;155(4):448–454.
  9. Rzany B, Mockenhaupt M, Baur S, et al. Epidemiology of SJS/TEN in Germany: population-based registry. J Clin Epidemiol. 1996;49(7):769–773.
  10. Roujeau JC, Kelly JP, Naldi L, et al. Medication use and risk of SJS/TEN. N Engl J Med. 1995;333(24):1600–1607.
  11. Sassolas B, Haddad C, Mockenhaupt M, et al. ALDEN algorithm for drug causality in SJS/TEN. Clin Pharmacol Ther. 2010;88(1):60–68.
  12. Seminario-Vidal L, Kroshinsky D, Malachowski SJ, et al. Supportive care guidelines for SJS/TEN in adults. J Am Acad Dermatol. 2020;82(3):539–551.
  13. Su SC, Mockenhaupt M, Wolkenstein P, et al. IL-15 is associated with severity and mortality in SJS/TEN. J Invest Dermatol. 2017;137(5):1065–1073.
  14. Viard I, Wehrli P, Bullani R, et al. Inhibition of TEN by CD95 blockade with human IVIg. Science. 1998;282(5388):490–493.
  15. Yang MS, Lee JY, Kim J, et al. Incidence of SJS and TEN in Korea: nationwide study. PLoS ONE. 2016;11(10):e0165933.
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