Unicentric Castleman's Disease Presenting As Back Pain.

Castleman's disease is a rare disorder caused by a polyclonal proliferation of B lymphocytes and plasma cells. Half of all cases of multicentric Castleman's disease are associated with HIV or Kaposi's Sarcoma. Typically, unicentric Castleman's disease presents as an enlarged thoracic lymph node but can present in multiple other body areas, such as the head and neck. This case report presents a rare large extrathoracic mass causing back pain in a 71-year-old man.