Ms. Castleman, a retired teacher and interior decorator, says she never has seen anyone have a heart attack dancing, but she can think of worse ways to die.

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Generally, people with unicentric Castleman disease aren't infected with HHV-8.

CNN: Castleman disease

Infection by a virus called the human herpesvirus 8 (HHV-8) is associated with Castleman disease, and doctors suspect that it may play a role, especially in multicentric Castleman disease.

CNN: Castleman disease

The immune system cells produce a protein called interleukin-6 (IL-6) that contributes to the overgrowth of lymphatic cells and leads to many of the signs and symptoms of Castleman disease.

CNN: Castleman disease

Liz Castleman, 71, a native of Gary, Ind.

WSJ: Not Content to Sit on Porch, Florida Retirees Rock On

It's not clear what causes Castleman disease.

CNN: Castleman disease