The skin's secret script: fingerprints of CD34 and the dolphin dance of Schwann cells

Abstract

Segmental neurofibromatosis (SNF), or Riccardi type V, is an uncommon mosaic variant of neurofibromatosis type 1, arising from postzygotic mutations in the NF1 gene. It reveals itself through dermatomally confined clusters of neurofibromas, usually in the absence of systemic features or family history. A 55-year-old woman presented with multiple, progressively enlarging papulonodular lesions localized to the left upper arm. Histopathological analysis demonstrated a non-encapsulated dermal spindle cell tumor with elongated, wavy, buckled nuclei-reminiscent of “diving dolphins”-set within a fibro-myxoid, mast cell-rich stroma. Immunohistochemistry further refined the picture: Schwann cells showed diffuse S100 positivity, while CD34 staining unveiled the delicate “fingerprint” pattern of dendritic fibroblasts. Taken together, these findings confirmed the diagnosis of neurofibroma. The segmental distribution and absence of systemic features established the diagnosis of SNF. The lesions were excised sequentially using elliptical incisions, leading to uneventful recovery and satisfactory cosmetic results. This case underscores the diagnostic value of correlating clinical distribution with distinctive microscopic clues. The dermatomal clustering of lesions, the evocative “diving dolphin” nuclei, and the CD34 fingerprint pattern together form a compelling diagnostic triad of SNF. Awareness of these features helps avoid misclassification among spindle cell tumours and ensures that management remains both accurate and tailored to patient needs.