Factitious Dermatitis Due to Thermal Burn With Histologic Features Simulating Fixed Drug Eruption.

Factitious dermatitis (FD) (dermatitis artefacta) is rare and often difficult to diagnose because of conflicting history and nonspecific clinical and histologic findings. It can present with varied clinical features including geometric ulcers, erosions, and less commonly bullae secondary to external trauma from chemicals, electric burns, heat, and suction. Herein, we describe a case of bullous FD due to thermal burn with histologic features demonstrating overlap with fixed drug eruption. Histopathology demonstrated a subepidermal blister with epidermal necrosis along with pigment incontinence and dermal eosinophils and neutrophils. Although these features, and the clinician's impression, were suggestive of fixed drug eruption, several morphologic findings allowed accurate diagnosis of FD: sharp demarcation of necrotic keratinocytes from adjacent uninvolved epidermis, elongated keratinocytes reminiscent of thermal or electrical artifact, and multinucleated keratinocytes. Although FD is often considered a diagnosis of exclusion, these clues may help dermatopathologists distinguish this entity from inflammatory dermatoses.