Table 6 Differentiating features between drug-induced phototoxic, photoallergic and photodistributed Steven’s–Johnson syndrome and toxic epidermal necrolysis
UVR reaction type | Phototoxic | Photoallergic | Photodistributed SJS/TEN |
|---|---|---|---|
Incidence | High | Low | Low |
Pathophysiology | Direct tissue injury | Type IV hypersensitive reaction | Type IV hypersensitive reactiona |
Sensitization Required | No | Yes | Yes |
Required dose of medication | High | Low | Low |
Cross-reactions to related agents | Low | High | Mediumb |
Agent type | Oral > topical | Oral < topical | Oral > topical |
Onset after light exposure | < 24 h (less common > 24 h) | > 24 h | > 24 h |
Progression / worsening of rash | 24–48 h | 48–72 h | > 48 h (up to week(s)) |
Clinical skin appearance | Exaggerated sunburn | Eczematous / Dermatitis | Photodistributed erythematous macules and flat atypical target lesions with vesicles/bullae and confluence of lesions |
Distribution | Only UVR exposed areas | UVR exposed areas; may spread outside UVR areas | UVR exposed areas; may spread outside UVR areas |
Palmar and plantar erythema | Uncommonc | Uncommonc | Common |
Mucous membrane involvement | Uncommonc | Uncommonc | Always |
Nikolsky sign | Negativec | Negativec | Positive |
Histology | Necrotic keratinocytes, predominantly lymphocytic and neutrophilic dermal infiltrate | Epidermal spongiosis, exocytosis of lymphocytes and perivascular inflammatory infiltrate | Subepidermal blisters with widespread necrosis (full thickness) and apoptotic keratinocytes associated with minimal lymphocytic inflammatory infiltrate |
Direct Immunofluorescence | Negative | May be positived | Negative |