“…Rare systemic proliferative non-infectious conditions and neoplastic conditions such as histiocytositic conditions, sarcoidosis, melanoma, leukemia/lymphoma, and metastasis often can be diagnosed based on pathological changes in other tissues or organs, but these sometimes lack and typical synovial tissue pathological changes may yield a diagnosis (76–78). Histiocytic conditions, such as multicentric reticulohistiocytosis, Langerhans cell histiocytosis, and Erdheim–Chester disease, typically involve tissue infiltration of bones, the reticuloendothelial system and various organs (79–83).…”