Primary cutaneous Rosai-Dorfman disease; a case-based review of a diagnostically and therapeutically challenging rare variant.

Primary cutaneous Rosai-Dorfman disease is a rare form of Rosai-Dorfman disease limited to the skin. The diagnosis of primary cutaneous disease is based on a combination of clinical presentation, histopathology, and the detection of S100+, CD68+, and CD1a- histiocytic immunophenotyping. However, the diagnosis of primary cutaneous disease is often difficult and significantly delayed due to the non-specific nature of its histologic and clinical features. In this review, we describe four cases in order to familiarize pathologists and dermatopathologists with the clinicopathologic correlation of primary cutaneous Rosai-Dorfman disease and to help facilitate early diagnosis. In addition, we discuss the proposed pathophysiology and molecular etiology of this tumor, and its relationship with IgG4 sclerosing disease.