What are characteristics of Dercum disease?

Dercum disease, also known as adiposis dolorosa, is characterized primarily by the presence of painful fatty masses, which are indeed benign. These masses often develop subcutaneously and can vary in size. The disease is also associated with a variety of systemic symptoms, including pain, which is a defining characteristic of the condition.

In the context of the question, the presence of these benign fatty tumors is the hallmark of Dercum disease, distinguishing it from other disorders that may involve muscle mass loss, fatigue, or changes in bone density. While individuals with Dercum disease may experience other symptoms, the defining characteristic that directly relates to the disease's identification is the formation of these benign fatty masses.