Background: Categorization of biopsy specimens into inflammatory reaction patterns is central to dermatopathologic assessment. Mixed inflammatory patterns are poorly characterized and may represent clinicopathologic challenges. The purpose of this study was to identify clinical and histopathologic findings associated with the mixed spongiotic-interface dermatitis (SID) histopathologic pattern.

Methods: Fifty-one institutional biopsy specimens of SID were identified over a 2-year period by retrospective natural language search. Histopathologic and clinical features were identified.

Results: The most common histopathologic features associated with SID were mild spongiosis (51%), focal vacuolar interface change (72%), lymphocytic exocytosis (92%), and superficial-dermal lymphocytic infiltrate (94%) with variable eosinophils (61%). Clinically, 80% of subjects presented with a symmetric morbilliform eruption. Polypharmacy (94%), immunosuppression (47%), and history of malignancy (47%) were common. The most common diagnoses were drug reaction (37%), possible drug reaction (12%), and viral exanthem (12%). Drug reaction with eosinophilia and systemic symptoms represented 25% of all confirmed cutaneous adverse drug reactions (CADR). Average time from drug initiation to symptom initiation was 20 days (SD: 22.3, range: 0-90); median disease duration was 25.5 days. Spongiotic vesicles and Langerhans cells were less common in patients with a strong clinicopathologic diagnosis of drug reaction compared to non-drug eruptions (p = 0.04).

Conclusions: The mixed SID pattern is commonly encountered in CADR but may represent a more subacute course, implying consideration for inciting medication(s) started before the typical 7- to 14-day window.

The authors declare no conflict of interest.

• UL1 TR002494/TR/NCATS NIH HHS/United States
• UL1TR002494/National Institutes of Health's National Center for Advancing Translational Sciences