Dermatology · Severe Cutaneous Adverse Reactions
The facts most likely to be tested
Stevens-Johnson Syndrome is a Type IV hypersensitivity reaction characterized by epidermal necrosis and mucocutaneous sloughing.
The diagnosis is defined by skin detachment involving <10% of the total body surface area (TBSA).
High-risk medications frequently implicated include allopurinol, anticonvulsants (carbamazepine, lamotrigine, phenytoin), sulfonamides, and nevirapine.
Clinical presentation typically begins with a prodrome of fever and flu-like symptoms followed by painful, dusky-red macules that progress to flaccid bullae.
A hallmark physical exam finding is a positive Nikolsky sign, where lateral pressure on the skin causes the epidermis to shear off.
Involvement of at least two mucosal surfaces (e.g., oral, ocular, or genital) is required for the diagnosis.
The most critical initial management step is the immediate discontinuation of the offending agent and transfer to a burn unit or intensive care unit for supportive care.
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A 34-year-old male presents to the emergency department with a 3-day history of fever, malaise, and a painful rash. Two weeks ago, he started taking carbamazepine for newly diagnosed seizures. Physical examination reveals diffuse, dusky-red macules on the trunk and face, with erosions on the lips and buccal mucosa. There is conjunctival injection and a positive Nikolsky sign on the upper back. The estimated area of skin detachment is approximately 7% of the total body surface area.
What is the most likely diagnosis?
Stevens-Johnson Syndrome
The patient exhibits the classic triad of drug exposure (carbamazepine), mucosal involvement, and <10% TBSA skin detachment, which defines Stevens-Johnson Syndrome.
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Etiology / Epidemiology
Triggered by medications (sulfa, lamotrigine, allopurinol) or Mycoplasma pneumoniae. Affects <10% of body surface area.
Clinical Manifestations
Prodrome of fever followed by mucosal involvement and targetoid lesions. Nikolsky sign positive.
Diagnosis
Clinical diagnosis confirmed by skin biopsy showing full-thickness epidermal necrosis.
Treatment
Immediate discontinuation of offending agent. Do not use corticosteroids.
Prognosis
High mortality risk; monitor for sepsis and multi-organ failure.
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Epidemiology & Etiology
Commonly triggered by sulfa drugs, allopurinol, lamotrigine, and anticonvulsants. Mycoplasma pneumoniae is the most frequent infectious trigger in children. Onset typically occurs 1–3 weeks after drug initiation.
Pertinent Anatomy
Involves the dermo-epidermal junction where keratinocyte apoptosis occurs. Mucosal involvement includes the oral, ocular, and genital surfaces, leading to severe scarring.
Pathophysiology
A Type IV hypersensitivity reaction mediated by CD8+ T-cells. Massive keratinocyte apoptosis leads to epidermal detachment from the basement membrane. This results in the classic blistering and sloughing of the skin.
Clinical Manifestations
Patients present with a flu-like prodrome followed by painful, dusky targetoid lesions. Mucosal involvement is mandatory for diagnosis, often causing severe stomatitis. Nikolsky sign (lateral pressure causing skin slippage) is a critical diagnostic indicator.
Diagnosis
Diagnosis is primarily clinical, but a skin biopsy is the gold standard to confirm full-thickness epidermal necrosis. Differentiate from SJS/TEN overlap by calculating BSA <10% for SJS, 10-30% for overlap, and >30% for TEN.
Treatment
The first-line intervention is immediate withdrawal of the causative agent. Supportive care in a burn unit is essential for fluid resuscitation and wound management. Corticosteroids are controversial and generally avoided due to increased infection risk.
Prognosis
Mortality is assessed using the SCORTEN scale. Key complications include sepsis, corneal scarring, and fluid/electrolyte imbalances. Long-term follow-up is required for ocular sequelae.
Differential Diagnosis
Toxic Epidermal Necrolysis: >30% BSA involvement
Erythema Multiforme: usually HSV-associated, lacks severe mucosal involvement
Staphylococcal Scalded Skin Syndrome: spares mucous membranes
Pemphigus Vulgaris: intraepidermal bullae, negative Nikolsky
Bullous Pemphigoid: subepidermal bullae, usually elderly