Rosai-Dorfman Disease of the Lung Overlapping with IgG4-related Disease: The Difficulty in Its Differential Diagnosis.

We herein report a case of Rosai-Dorfman disease (RDD) overlapping with IgG4-related disease (IgG4-RD), which presented as diffuse interstitial lung disease with a perilymphatic pattern, followed by submandibular gland and eyelid swelling. The pathological findings of the submandibular gland biopsy specimen were indicative of IgG4-RD alone. We diagnosed the patient with RDD with overlapping IgG4-RD. However, the optimal method for differentiating between these two entities is still controversial. It is important that clinicians are aware that RDD should be included in the differential diagnoses of diffuse interstitial lung disease with a perilymphatic pattern and that RDD can overlap with IgG4-RD.