Pathogenic Analysis of White Sponge Nevus Using Electron Microscopy

Objectives: White sponge nevus (WSN) is an autosomal dominant disorder which is characterized by white spongy plaques predominantly affects oral mucosa. Histopathological finding indicates thickening and extensive vacuolization of the spinous cell layers, intracellular edema, and acanthosis in the oral mucosa. Previous study indicated that point mutations encoding mucosal-specific keratins K4 and K13 genes causing WSN in familial cases. Keratins are intermediate filaments which are expressed in tissue specific manner. Mutations in keratin genes have been identified as inherited skin disorders such as epidermolysis bullosa simplex, pachyonychia congenita and bullous congenital ichthyosiform erythroderma (BCIE). Previously, ultrastructural analysis of WSN has been performed mainly in single case. The purpose of this study was to analyze pathogenesis of WSN by ultrastructural observations throughout the multiple cases.
Methods: We performed microscopic and electron microscopic analysis for 3 cases clinically diagnosed for WSN, 22 and 28-year-old females and 27-year-old male respectively.
Results: Thickened whitish lesion was seen on buccal mucosa dominantly in all patients. Biopsy showed thickened epithelium, showing hyperkeratosis and acanthosis with intact basal cell layer. The cells of spinous layer exhibit intracellular edema, so-called basket weave appearance. In these areas, eosinophilic materials were observed around the nuclei. Electron microscopy revealed aggregation of keratin filaments around nucluei in the upper layer of the epithelium in all cases. We compared the microscopic findings between the white sponge nevus with its skin counterpart, BCIE. Both WSN and BCIE showed similar morphologic features in histopathology and ultrastructure.
Conclusions: Keratins play an important role in mucosal epithelium regarding morphogenesis and maintenance of functions similar to that of skin.