What is the preferred biopsy technique to diagnose toxic epidermal necrolysis (TEN) or Stevens-Johnson syndrome (SJS)?

Preferred Biopsy Technique for SJS/TEN Diagnosis

Perform a full-thickness punch biopsy from lesional skin immediately adjacent to a blister and send for routine histopathology; simultaneously obtain a second biopsy from perilesional skin and send unfixed for direct immunofluorescence to exclude immunobullous disorders. 1

Biopsy Technique Details

Primary Biopsy (Histopathology)

• Location: Lesional skin just adjacent to a blister (not from the blister itself)
• Purpose: Confirms diagnosis by demonstrating full-thickness epidermal necrosis with subepidermal cleavage
• Expected findings: Multiple apoptotic keratinocytes throughout the epidermis, subepidermal split forming a bulla, and perivascular lymphocytic infiltrate in the dermis 1

Second Biopsy (Direct Immunofluorescence)

• Location: Perilesional skin (near but not in the blister)
• Handling: Must be sent unfixed for direct immunofluorescence
• Critical purpose: Excludes immunobullous disorders (pemphigus vulgaris, bullous pemphigoid, mucous membrane pemphigoid, paraneoplastic pemphigus, bullous lupus, linear IgA disease) which require different treatment strategies 1

Special Considerations in Children

In pediatric cases with diagnostic uncertainty between SJS/TEN and staphylococcal scalded skin syndrome (SSSS):

• Perform a shave biopsy of blister roof for frozen section as it is less invasive than full-thickness biopsy 2
• This distinguishes the plane of cleavage: intraepidermal (SSSS) versus subepidermal (SJS/TEN) 2
• If SSSS is clinically typical, no biopsy is required 2

Clinical Context

Important caveat: While biopsy confirmation is recommended in guidelines, the clinical diagnosis often precedes histopathological confirmation due to the rapidly progressive nature of the disease. The striking clinical presentation—widespread tender erythema, atypical targets, purpuric macules, positive Nikolsky sign, and severe mucositis—typically allows for provisional diagnosis and immediate management initiation 1.

Frozen Section Utility

Recent evidence suggests frozen-section diagnosis can provide same-day diagnostic confirmation and help predict disease progression, particularly useful when patients present with early erythema multiforme-like lesions 3. This technique can identify epidermal necrosis and GVHR-like findings (apoptotic keratinocytes, satellite cell necrosis) in unaffected sites, potentially predicting more aggressive disease behavior 3.

Practical Algorithm

1. Clinically suspect SJS/TEN based on tender skin, atypical targets, mucositis, and positive Nikolsky sign
2. Immediately obtain two biopsies:
   • One from lesional skin adjacent to blister → formalin-fixed for routine histopathology
   • One from perilesional skin → unfixed for direct immunofluorescence
3. Consider frozen section if rapid diagnosis needed or disease progression uncertain
4. In children with SSSS vs. SJS/TEN uncertainty: Shave biopsy of blister roof for frozen section
5. Do not delay treatment while awaiting histopathology results

The dual-biopsy approach is essential because immunobullous disorders can mimic SJS/TEN clinically and histologically (same subepidermal cleavage plane) but require fundamentally different immunosuppressive treatments rather than supportive care 1.