True histiocytic lymphoma with multiple skin nodules

A 73-year-old white woman developed multiple cutaneous nodules that fluctuated in size and occasionally regressed. The tumor cells infiltrating the dermis were histiocytic by light microscopy, marker studies, and electron microscopy. Similar cells were present in a bone marrow biopsy specimen. A diagnosis of true histiocytic lymphoma was made. The case illustrates some of the problems that may arise in evaluation of clinical and pathologic findings in a patient with a proliferative disorder of histiocytes and demonstrates the contribution that electron microscopy can provide in establishing the diagnosis.