Intrathoracic Rosai-Dorfman disease with spontaneous remission: a clinical report and a review of the literature.

Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is a rare non-neoplastic disease that is characterized by a proliferation of histiocytes mostly in lymph nodes. However, the etiological mechanism of RDD still remains unclear. Intrathoracic manifestations of RDD are only observed in 2% of patients with RDD. Spontaneous remission was reported in about 20% of patients with RDD; however, there are no reports of an intrathoracic manifestation of RDD that showed a spontaneous remission within a short period of time. A 64-year-old Japanese female with dry cough and left chest pain was introduced to our hospital, and computed tomography revealed a pulmonary nodular lesion and enlarged mediastinal lymph nodes. The bronchial specimen obtained from the abnormal mucosal lesion showed massive infiltration of histiocytes underneath the bronchial epithelium and emperipolesis, a typical pathological finding in RDD, which is characterized by the presence of histiocyte-like cells engulfing intact lymphocytes. These histiocytes were positive for S-100 (one of the known positive markers of RDD) and for CD68 (a marker for various cells of the macrophage lineage). All these findings are consistent with the diagnosis of RDD. These radiological and endoscopic findings spontaneously resolved within four months without any treatment. In conclusion, clinicians should be aware of this disease as one of differential diagnoses of pulmonary nodules in combination with mediastinal lymph node enlargements, especially in order to differentiate it from primary lung cancer.