Photodermatitis with minimal inflammatory infiltrate: Clinical inflammatory conditions with discordant histologic findings

Dermatoses associated with cutaneous photosensitivity are a group of photodistributed skin eruptions caused or exacerbated by light. Multiple clinical variants of photosensitive dermatoses have been characterized including polymorphous light eruption, chronic actinic dermatitis, solar urticaria, phototoxic and photoallergic dermatitis, reticular erythematous mucinosis, acute cutaneous lupus erythematosus, and dermatomyositis. As there may be significant overlap among the clinical presentation of these conditions, the specific diagnosis of individual photodermatosis relies heavily on characteristic histopathologic features. We present here 5 cases of photodistributed eruptions with virtual absence of histologic epidermal changes and dermal inflammation, yet all were described clinically as being "inflammatory" and erythematous. All cases of this "pauci-inflammatory photodermatitis" presented with photodistributed bright red macular erythema or slightly indurated plaques that developed over a period of weeks to months and clinically resembled photoallergic or phototoxic drug reactions or polymorphous light eruption. Microscopically, however, only very sparse dermal lymphocytic infiltrate was noted with no or minimal epidermal changes. To our knowledge, the observation of clinically evident photodistributed dermatoses that demonstrate such minimal histopathologic findings has not been reported. Clinicians and histologists should be aware of the disparity that may be encountered in this setting, as the clinical features are usually far more impressive than those seen histologically.