Primary cutaneous Rosai-Dorfman-Destombes disease with features mimicking IgG4-related disease: A challenging case report and literature review.

Rosai-Dorfman-Destombes disease (RDD) is a rare histiocytic disorder affecting lymph nodes as well as extranodal sites. Although cutaneous involvement in RDD is common, primary cutaneous RDD is a distinct and not well-documented entity with unknown aetiology and non-specific clinicopathological features. We report a case of a 57-year-old patient, who presented with an indolent skin nodule in the left sub-nipple area. Surgical excision was performed. Histological examination concluded to the diagnosis of cutaneous RDD with histological features mimicking IgG4-related disease. The diagnosis of systemic RDD with cutaneous involvement was ruled out after exclusion of extracutaneous involvement. No recurrence or systemic progression was observed during follow-up. The diagnosis of primary cutaneous RDD is very uncommon and hence is challenging for pathologist and dermatologist especially with features of IgG4-related disease. Careful systemic and microscopic examinations help in establishing the appropriate diagnosis.