What is the diagnostic approach for a patient with suspected Steven's Johnson syndrome?

Diagnosis of Stevens-Johnson Syndrome

Stevens-Johnson syndrome is diagnosed primarily through clinical assessment of characteristic skin and mucosal findings, supported by skin biopsy showing confluent epidermal necrosis, with immediate discontinuation of suspected culprit drugs being the most critical first step. 1

Clinical Diagnostic Criteria

The diagnosis requires recognition of specific cutaneous and mucosal features:

• Painful skin lesions that begin on the face and chest, progressing to widespread involvement with flat atypical target lesions, purpuric macules, or confluent erythema 1
• Epidermal detachment quantified by body surface area (BSA): SJS <10% BSA, SJS/TEN overlap 10-30% BSA, TEN >30% BSA 1, 2
• Positive Nikolsky sign where epidermis shears away with minimal lateral pressure on apparently uninvolved skin 1, 3
• Flaccid blisters that rupture easily, leaving denuded dermis with sheets of detached epidermis 1
• Mucosal involvement affecting two or more sites (eyes, mouth, nose, genitalia) with purulent keratoconjunctivitis, oral erosions, and genital lesions 1

Essential History Components

Document these specific elements immediately:

• Prodromal symptoms including fever, malaise, and upper respiratory tract symptoms occurring 1-3 days before rash onset 1, 2
• Complete medication history for the preceding 2 months, including all prescription drugs, over-the-counter medications, herbal remedies, and complementary therapies with exact start dates 1, 4
• Index date when the first symptom appeared and detailed progression timeline of the eruption 1, 4
• Respiratory symptoms such as cough, dyspnea, bronchial hypersecretion, or hemoptysis indicating airway involvement 1
• Gastrointestinal symptoms including diarrhea suggesting bowel involvement 1

Physical Examination Findings

Perform systematic assessment of all body systems:

• Skin examination documenting percentage BSA with epidermal detachment, presence of target lesions versus atypical targets, and areas of confluent erythema 1
• Mucosal assessment of eyes (conjunctival injection, pseudomembrane formation), oral cavity (erosions, hemorrhagic crusting), and genitalia (erosions, urethral involvement) 1
• Vital signs including temperature, oxygen saturation, blood pressure, and heart rate 1
• Baseline body weight for fluid resuscitation calculations 1

Histopathological Confirmation

Skin biopsy is necessary to support clinical diagnosis and exclude other blistering disorders:

• Take biopsy from lesional skin adjacent to a blister showing variable epidermal damage ranging from individual cell apoptosis to confluent epidermal necrosis 1
• Characteristic findings include basal cell vacuolar degeneration, subepidermal vesicle or bulla formation, and mild perivascular lymphocytic infiltrate in the dermis 1, 5
• Second biopsy for direct immunofluorescence from periblister lesional skin to exclude immunobullous disorders like pemphigus or pemphigoid 4

Laboratory Investigations

Obtain comprehensive baseline studies:

• Complete blood count looking specifically for lymphopenia, which is characteristic 1, 3
• Metabolic panel including urea, electrolytes, magnesium, phosphate, bicarbonate, and glucose 4
• Liver function tests and coagulation studies 4
• Inflammatory markers including ESR and C-reactive protein 4
• Blood cultures if the patient is febrile to distinguish drug reaction from sepsis 1
• Skin swabs for bacterial and candidal culture from lesional areas 1

Severity Assessment

Calculate SCORTEN within 24 hours of admission to predict mortality risk:

The SCORTEN score uses seven independent risk factors (age >40 years, malignancy, tachycardia >120 bpm, initial BSA detachment >10%, serum urea >10 mmol/L, serum glucose >14 mmol/L, serum bicarbonate <20 mmol/L), with mortality ranging from 1% (score 0-1) to >90% (score ≥5) 1, 4, 2

Distinguishing SJS from Similar Conditions

Differentiate from erythema multiforme major (EMM):

• EMM features typical target lesions or raised atypical targets predominantly on limbs and extremities, whereas SJS shows flat atypical targets with widespread distribution 1
• EMM etiology is mostly related to herpes simplex virus reactivation, while SJS/TEN is usually drug-triggered 1
• Mycoplasma-associated mucositis may present with predominantly mucosal involvement and minimal cutaneous lesions, particularly in children 1

Critical Pitfalls to Avoid

Common diagnostic errors that delay appropriate management:

• Waiting for biopsy results before discontinuing suspected drugs—clinical diagnosis should prompt immediate drug cessation 1, 4
• Misdiagnosing as simple drug eruption when early lesions are not yet confluent or blistering 6
• Overlooking mucosal involvement by failing to examine all mucosal surfaces including genitalia 6
• Attributing fever to infection rather than recognizing it as part of the SJS/TEN syndrome itself 1
• Delaying transfer to specialized care while awaiting confirmatory testing—suspected cases require immediate transfer to burn centers or ICUs 4, 6

Immediate Actions Upon Diagnosis

Once SJS/TEN is suspected clinically:

• Discontinue all potential culprit drugs immediately without waiting for biopsy confirmation 1, 4
• Arrange urgent transfer to a burn center or ICU with multidisciplinary expertise for patients with >10% BSA involvement 4, 6
• Initiate supportive care including fluid resuscitation, temperature control, and wound care protocols 4
• Consult ophthalmology within 24 hours for all patients with ocular involvement 4, 7