Clear cell fibrous papule pathology

Introduction

Clear cell fibrous papule is a rare variant of fibrous papule that has a clinical presentation identical to conventional fibrous papule of the nose. Its unusual morphology and rarity can cause diagnostic confusion.

Histology of clear cell fibrous papule

In clear cell fibrous papule, the epidermis may be normal or show some degree of hyperkeratosis (figures 1,2). The dermis is expanded by a proliferation of clear cells arranged in sheets, clusters, or as single cells (figures 3,4). The clear cells show variation in size and shape. The nuclei are small and round without pleomorphism, hyperchromasia, or mitoses. The nuclei may be centrally located or may be eccentrically displaced by a large intracytoplasmic vacuole (Figures 3,4). Some clear cells may exhibit finely vacuolated cytoplasm with nuclear scalloping.

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Special studies for clear cell fibrous papule

Immunohistochemistry of clear cell fibrous papule shows the clear cells are diffusely positive for vimentin and negative for cytokeratin AE1/AE3, epithelial membrane antigen, carcinoembryonic antigen, and HMB-45. S-100 protein often is negative but may be focally positive.

Differential diagnosis of clear cell fibrous papule

Other diagnoses to be considered include:

• Balloon cell naevus — this shows positivity with melanocytic markers with immunohistochemistry
• Clear cell hidradenoma — this shows positivity with cytokeratin and ductal differentiation
• Other clear cell tumours — a panel of immunohistochemistry studies can be used to exclude other possibilities. The clinical presentation can be an important clue in diagnosing clear cell fibrous papule.