CD34-reactive trichodiscoma

Background: Trichodiscomas are rare hamartomas of the dermal portion of the hair disc, a specialized component of the perifollicular mesenchyme. They are usually found as asymptomatic multiple skin-colored papules on the face and extremities and may have an autosomal dominant inheritance pattern. However, a solitary variant has been described. Case report: A 78-year-old woman presented with a single, non-pigmented, firm papule on the left tip of the nose, measuring 3.5 mm in diameter. Results: The histological examination revealed the previously described features of a trichodiscoma. The immunohistochemical analysis showed strong immunoreactivity for CD34 in the spindle cell component. Spindle cells were negative for S-100, HMB-45, Melan-A, EMA, neurofilament, desmin, and Factor XIIIa by immunohistochemistry. Conclusions: We report strong reactivity for CD34 in the spindle cell component of a trichodiscoma. We suggest that this lesion be considered in the differential diagnosis of any CD34 ⁺ dermal spindle cell proliferation, in which an adjacent epithelial component cannot be entirely excluded.