LAUSR

As the original consulting dermatopathologist for this case, I read with great interest the article by Kuzyk et al, titled “A Case Indistinguishable Between Indeterminate Cell Histiocytosis and Cutaneous Rosai-Dorman Disease,” and would like to offer a different opinion. The authors based their diagnosis on histiocytoid cells within the dermis that were CD68, S100, and CD1a. Electron microscopy was not performed. They quoted several articles reporting patients with indeterminate cell histiocytosis (ICH) may have lesions with cells that are CD68, S100 and CD1a, unlike the original description of a patient with lesions that contain cells that are CD68, S100, and CD1a and lack Birbeck granules by electron microscopy. They hypothesised that these non-Langerhan histiocytoid cells lose their CD1a positivity depending on the course of the disease. In 1985, Wood et al said, for the first time, “the indeterminate cell is a histiocyte that is morphologically and antigenically similar to the Langerhans cell although it lacks Birbeck granules.” Based on my initial review of this case, it was my professional opinion that the diagnosis was neither ICH nor cutaneous Rosai-Dorman disease (CRDD) but rather xanthogranulomatosis. Subsequent review of the slides following the publication by Kuzyk et al reaffirmed my initial diagnosis. The presence of histiocytes with glassy cytoplasm and a milieu of inflammatory cells, including eosinophils, neutrophils, and lymphocytes, are typical findings seen in xanthogranulomas. The histiocytes were CD68, S100, and CD1a, which confirms my diagnosis. There was no evidence of emperipolesis excluding a diagnosis of CRDD. Since most xanthogranulomas have classic morphology, immunoperoxidase stains are rarely done and thus we do not know the true expression of S100 histiocytes in these lesions. Tomaszewski et al described S100 histiocytes in approximately 25% of xanthogranulomas. The negative CD1a suggests that these cells are S100 protein-positive histiocytes, rather than indeterminate cells or Langerhans cells and do not support the diagnosis of ICH or CRDD. Rather, the morphological findings fulfill all the criteria for xanthogranuloma. S100 protein is a very nonspecific immunoperoxidase stain and can show positivity in melanocytes, dermal dendrocytes, histiocytes, Schwann cells, and so on. Even Ratzinger et al acknowledged, “We even think that all non-Langerhans cell histiocytosis are variants on xanthogranuloma.” If indeterminate cell histiocytosis exists, then it should be reserved for patients who have lesions with cells that are CD68, S100, and CD1a and lack Birbeck granules by electron microscopy. When I was a fellow with the late Dr A. Bernard Ackerman, he was known to say, “If it looks like a duck, walks like a duck and quacks like a duck, the chances are it is a duck.”