The reason it develops in some people is unknown. It is not an inherited or contagious disease.
Patients have an overgrowth of bone marrow cells, called plasma cells.
The symptoms and potential complications of these diseases are very different. Some patients have a co-existing disorder, called Castleman's disease, which is an abnormality of the lymph nodes. Though the majority of patients have abnormal bone x-rays, most will not have bone pain. In order to have the syndrome, you do not need to have all the features. Its cause is not known.