Abstract
A 90-year-old female was referred to our hospital for a mass of 28×35 mm in diameter and irregularly shaped pigmentation existing on the left big toe. The tumor was gradually growing with an ulcerated surface, causing bleeding and gait disturbance. Because the left inguinal lymph nodes were swollen, computed tomography (CT) was performed considering lymph node metastases. However, CT examination revealed no abnormal findings in the internal organs, except swollen lymph nodes on the left inguinal area. Biopsy was carried out, showing that the tumor was mainly composed of spindle tumor cells with nuclear atypia and mitosis. Although immunohistochemical studies including various antibodies were done, immunoreactivity was demonstrated mainly with anti-S100 and SOX10 despite negative with other antibodies including MITF and H3K27me3. Histology of adjacent pigmentation revealed no findings suggestive of malignant melanoma (MM). These studies showed the tumor was diagnosed as malignant peripheral nerve sheath tumor (MPNST) lacking of other clinical symptoms of neurofibromatosis-1. Amputation of toe was proposed, but the patient refused the procedure. Therefore, we suggested an application of Mohs paste with subsequent shaving of the tumor, which led to the flattening and shrinkage. Subsequently, she agreed to the resection under a local anesthesia. Histology of the resected lesion showed only a necrotic change without S100 and SOX10 positive cells. Postoperatively, neither tumor recurrence nor distant metastases were recognized during the two-year of follow-up period.
MPNST, especially arising on the acral sites, is a rare malignancy. In addition, histological findings are occasionally difficult to discriminate from tumors including desmoplastic MM and other mesenchymal origin. Although surgery including amputation is the primary treatment, it cannot always be acceptable for the patients like those with an inoperable condition. Therefore, it is suggested that Mohs paste as a presurgical application is beneficial for inoperable patients including elderly patients.
