[2] Some symptoms that are commonly seen in HHV-8-associated MCD and iMCD like extravascular fluid accumulation (peripheral edema, ascites, pleural effusions), and enlargement of the liver and/or spleen are uncommon in UCD.

[3] UCD is associated with increased risk of paraneoplastic pemphigus[3] as well as bronchiolitis obliterans (BO), AA amyloidosis, vascular neoplasms (e.g., FDC sarcoma), and possibly lymphomas.

Cases of Castleman disease running in families have been reported; however, no causative genetic variants have been identified[5] The mechanism of UCD is poorly understood.

Most published research supports a growth of abnormal immune system cells (neoplasm) as the most likely cause of UCD, but this has not been conclusively demonstrated or fully characterized.

[5] Systemic symptoms and laboratory abnormalities may be associated with the presence of plasmacytic features on microscopic analysis of affected lymph node tissue.

[citation needed] UCD is diagnosed based on patient history, physical exam, laboratory testing, radiologic imaging, and microscopic analysis (histology) of biopsied tissue from an enlarged lymph node.

[3] The microscopic appearance (histology) of biopsied tissue from an enlarged lymph node must demonstrate a constellation of features consistent with Castleman disease.

[8] Occasionally, surgical removal of an enlarged lymph node may be prohibitively high risk at the time of diagnosis due to large size or proximity to critical structures.

[10] Most people with UCD who undergo complete surgical resection of enlarged lymph nodes achieve long-term disease-free survival, with an observed ten-year mortality of 4% in the largest case series to date.