A case of multinucleate cell angiohistiocytoma in a 14‐year‐old boy showing two different clinical and histopathological findings

Multinucleate cell angiohistiocytoma (MCAH) is a rare cutaneous disease entity characterized by multiple red-to-brown or violaceous papules usually located on the acral regions, such as the face and the distal arms and legs. It affects elderly women more than men and rarely occurs at a young age. The exact pathogenic mechanism of MCAH is not yet clearly understood. We report an exceptionally rare case of a 14-year-old boy who presented with multiple asymptomatic erythematous papules and a single flat brownish plaque on the left chest. The brownish plaque lesion histologically showed proliferation of dilated small vessels in the upper-mid dermis and numerous oddly shaped multinucleate cells intermingled with lymphocytes and macrophages. The erythematous papules also showed dilated small vessels in the upper-mid dermis and multiple interstitial histiocytic infiltrations, but no multinucleate cells were detected. In immunohistochemistry studies, CD68 and vimentin staining were positive for both specimens. Based on the clinicopathological findings and immunohistochemistry studies, MCAH was diagnosed. To the best of our knowledge, this is the first case report of MCAH occurring in young age and showing two different clinical and histological phases at the same time.