Spongiform pemphigoid: A case series of an uncommon histopathologic pattern.

Introduction: Bullous pemphigoid is an autoimmune bullous disease characterized by subepidermal separation. We encountered cases of bullous pemphigoid confirmed by direct immunofluorescence study but demonstrating spongiotic dermatitis without subepidermal clefting. Many of them occurred in volar sites, mimicking dyshidrotic dermatitis.

Methods: We retrospectively collected patients who were pathologically and/or immunopathologically diagnosed with bullous pemphigoid from 2002 to 2017. Patients who presented with prominent spongiosis without subepidermal clefting were included and compared with patients who were diagnosed with dyshidrotic dermatitis.

Results: A total of nine cases of spongiform pemphigoid out of 385 bullous pemphigoid patients (2.3%) were identified and compared with 15 patients with dyshidrotic dermatitis. Average age of spongiform pemphigoid patients (76 years) was much older than that of the control group (34 years). Microvesicles in the mid- to lower epidermis (P < 0.001), eosinophils exocytosis (P < 0.001), and eosinophils microabscess (P < 0.001) in both the epidermis and papillary dermis were more common in spongiform pemphigoid.

Conclusion: Spongiform pemphigoid mimics spongiotic dermatitis may result in a pathological diagnostic pitfall. The presence of eosinophil microabscess and exocytosis in the epidermis and papillary dermis were important clues. Immunofluorescence studies should be conducted to confirm the diagnosis of bullous pemphigoid.