Thyroid Rosai-Dorfman disease with infiltration of IgG4-bearing plasma cells associated with multiple small pulmonary cysts

BACKGROUND: Rosai-Dorfman disease (RDD) is a rare histiocytosis which involves principally lymph nodes. Thyroid involvement in RDD is a very rare situation, and lung involvement is even rarer. CASE PRESENTATION: We report the case of a 46-year-old woman presenting a painless mass in the right side of the neck and subacute dyspnoea. Computerised tomography (CT) scans of the neck and thorax showed a large thyroid mass causing tracheal stenosis and multiple cystic lesions in both lungs. Subtotal thyroidectomy with a tracheal segment resection and histological analysis confirmed the diagnosis of nodal and extranodal (thyroid, tracheal and probably lung) Rosai-Dorfman disease (RDD) with the presence of increased numbers of IgG4-bearing plasma cells. Clinical, functional and radiological follow up 4 years after surgery without medical treatment did not show any disease progression. CONCLUSIONS: This case report indicates a benign course of nodal RDD with thyroid and tracheal infiltration following surgical resection, association of typical histological signs of RDD (emperipolesis) with IgG4-related disease features, and that lung cysts might be a manifestation of RDD.