White sponge nevus mimicking intraoral white lesion on the buccal mucosa: A case report

White sponge nevus (WSN) is a rare autosomal dominant disorder, which is characterized by soft white mucosal plaques in the oral cavity and other regions. The white plaques exhibit surface irregularities, involving a wrinkly or spongy pattern. Its histopathological findings included a thick stratified squamous epithelium, which displays parakeratosis; cytoplasmic clarification and vacuolization in the stratum spinous layer cell, which were caused by swelling of the cytoplasm; and nuclear condensation. The widely accepted theory for the cause of the onset of WSN is mutation of the keratin 4 and/or 13 genes. We present a case of WSN, in which the patient, a Japanese female, exhibited white plaques on her bilateral buccal mucosae. A 56-year-old female visited our hospital, and her chief complaint was a white lesion on the buccal mucosa. White lesions were observed on her bilateral buccal mucosae. The lesions were widespread and spongy and had irregular surfaces. Tissue samples were obtained during biopsies performed at our hospital. The lesions’ histological findings included epithelial hyperparakeratosis with vacuolated cytoplasm in the spinous layer, but there was no evidence of epithelial dysplasia. In addition, spinous layer cells were nuclear condensation and perinuclear acidification. The final histological diagnosis was WSN; thus, we decided to follow-up the patient’s progress. Recently, a few studies have reported on the malignant transformation of WSN. Therefore, it is necessary to monitor patients with WSN regularly, and to investigate more cases of WSN to elucidate the cause of such transformation.