Casleman Disease is a condition which leads to lymph node enlargements and dysfunction. It was first described in 1956, and since then three types have been identified :
• Unicentric Castleman disease (UCD)
• Idiopathic multicentric Castleman disease (iMCD)
• Human herpesvirus 8 associated multicentric Castleman disease (HHV-8-associated MCD).
The cause or causes of the first two types are unknown, although it's presumed to be an auto-immune problem. The third type is associated with infections of the human herpes-virus 8 (HHV-8) and in the vast majority of cases do not lead to any disease. It's estimated that 10 - 40% of people worldwide are permanently infected, but their immune system suppresses any symptoms. The reason why the virus initiates Castleman in some individuals is unknown.
Note: The prevalence of the disease (outside the US, where there are more than 6,000 cases per year) is also unknown.
More info : The Castleman Disease Collaborative Network