Interstitial Granulomatous Dermatitis with Plaques

An 8‐year‐old male presented with several 1–4 cm, indurated, brownish‐red nodules with superficial, punctate hemorrhagic crusts localized to the groin, which developed over several weeks. An initial biopsy was consistent with Langerhans cell histiocytosis. A work up, including a chest and abdominal CT scan demonstrated a large mediastinal mass which was diagnosed as precursor T cell lymphoblastic lymphoma. Treatment with a chemotherapeutic protocol resulted in shrinkage of both the mediastinal and cutaneous lesions. Late in the course of treatment the cutaneous lesions rapidly recurred and spread to various sites. A second skin biopsy showed an extensive diffuse infiltrate of histiocytic‐appearing cells extending from the papillary dermis into the superficial subcutis. The cells had markedly pleomorphic, vesicular nuclei and abundant amphophilic cytoplasm. Numerous mitotic figures were present. The neoplastic cells were S‐100 protein and CD1a positive by immunohistochemistry. The histopathologic diagnosis was Langerhans cell sarcoma. Gene rearrangement studies demonstrated clonal rearrangement of the T cell receptor gamma gene in specimens from both the mediastinal mass and one of the recurrent cutaneous lesions. The sizes of the PCR products were identical demonstrating a clonal relationship between the two neoplasms.