Epithelioid Blue Nevus

Histopathology Epithelioid blue nevus (EBN) is a tumor with indistinct boundaries located in the dermis (Fig. 1A). EBN can penetrate the fat layer, and often affects the appendages. Variably sized spherical cells and polygonal cells are present in the spaces between collagenous fibers.1 Spherical cells have evident pigmentation, a bubble-shaped nucleus, and an obvious nucleolus. Polygonal cells show little pigmentation, but also have a bubble-shaped nucleus and an evident single nucleolus (Fig. 1B and 1C). Scattered mitosis is sometimes observed.Figure 1: Hisptopathological characteristics of epithelioid blue nevus. A: The tumor with indistinct boundaries is located in the dermis (×40). B and C: Spherical cells with evident pigmentation, a bubble-shaped nucleus, and an obvious nucleolus. Polygonal cells show little pigmentation, but also have a bubble-shaped nucleus and a single nucleolus (B and C: ×100).Immunohistochemistry reveals CD68 expression in the spherical cells. Epithelioid cells have S-100 and HMB-45 expressions, but no CD68 expression. EBN must be distinguished from pigment-synthesizing melanoma (animal melanoma). Pigment-synthesizing melanoma may involve the skin, but has more obvious cellular atypia and mitosis than EBN.2 It is widely accepted that EBN is benign, whereas pigment-synthesizing melanoma is malignant. However, some scholars have classified both EBN and pigment-synthesizing melanoma as pigment epithelioid melanocytoma.3 Pigment epithelioid melanocytoma is believed to have low malignant potential, but has a better prognosis than the traditional melanoma with consistent stages.4 Clinical features EBN is a rare variant of blue nevus that often develops in patients with Carney complex.1 However, EBN can also exist independently of Carney complex. Carney complex is a rare autosomal dominant disease. In addition to the presence of a blue nevus, Carney complex is accompanied by skin pigmentation, myxoma, Cushing's syndrome, acromegaly, sexual precocity, and melanotic schwannoma. EBN often occurs on the trunk and limbs, and may also involve the oral and genital mucosa. EBN generally occurs independently and may occur at several locations. EBN manifests clinically as a round papule or nodule that is blue-black to purple in color5 (Fig. 2). The diameter of an EBN skin lesion can be as large as 1 cm. EBN cannot be treated with oral or topical medications. Surgical removal is needed.Figure 2: The clinical manifestation of epithelioid blue nevus. The lesion presents as a single blue-black papule with a diameter of about 5 mm on the left acrotarsium.