Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Overview / DefinitionStevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) represent a spectrum of severe cutaneous adverse reactions. SJS is defined as epidermal detachment affecting less than 10% of body surface area (BSA), while TEN involves more than 30% of BSA. Both conditions are characterized by mucosal involvement and a systemic inflammatory response.EpidemiologySJS and TEN are rare but serious conditions, with an incidence of approximately 1-2 cases per million people per year. They can affect individuals of any age but are more common in adults. A higher prevalence is noted in patients with certain genetic predispositions, particularly in those of Asian descent.Incidence: 1-2 cases/million/yearAge: More common in adultsGenetic predisposition: Higher in Asian populationsPathophysiology / MechanismThe pathophysiology of SJS and TEN involves a complex immune-mediated response. Drug-induced hypersensitivity leads to keratinocyte apoptosis mediated by CD8+ T cells and various cytokines. This results in epidermal necrosis and subsequent detachment. Common triggers include:Medications (e.g., anticonvulsants, sulfonamides, allopurinol)Infections (e.g., Mycoplasma pneumoniae, herpes simplex)Vaccinations and malignanciesClinical PresentationPatients typically present with prodromal symptoms such as fever, malaise, and sore throat, followed by the rapid onset of a painful rash. The rash progresses to vesicles and bullae, leading to epidermal detachment. Mucosal involvement is often present, affecting the oral, ocular, and genital regions.Prodromal symptoms: Fever, malaise, sore throatRash: Painful, vesicular, bullousMucosal involvement: Oral, ocular, genitalDiagnosis / WorkupDiagnosis is primarily clinical, based on the history of drug exposure and characteristic signs. A skin biopsy may be performed to confirm the diagnosis, revealing full-thickness necrosis of the epidermis. Laboratory tests may include:Complete blood count (CBC) to assess for leukope