Kristy Smith of Gloucester once raised tens of thousands of dollars for people living with diabetes, but now she has to use those fundraising skills for herself as she battles a rare disease.

An experimental stem cell treatment offered by a doctor in Arizona is the only option currently available for Smith hoping to cure her Dercum’s disease, one of the rarest diseases in the world with no FDA-approved cure.

Smith was forced to resign her job as chief executive district manager for Subway in 2017 when her diagnosis became clear. “You look fine on the outside but it wreaks havoc on the inside,” she said of the ailment which she said is the third rarest in the world. Her case is even more abnormal, as the disease usually only occurs in older or obese women. Smith went from running marathons to being unable to walk too quickly without pain.

Dercum’s disease is characterized by small, fatty tumor growth throughout the tendons, ligaments and subcutaneous tissue of...