Longtime civil rights activist and former presidential candidate Rev. Jesse Jackson disclosed today that he’s been diagnosed with Parkinson’s Disease, the Associated Press reports.

In a letter to supporters, Jackson said he’s been receiving outpatient treatment for two years and now plans to dedicate himself to physical therapy to battle the often-debilitating disease.

“Recognition of the effects of this disease on me has been painful, and I have been slow to grasp the gravity of it,” he wrote. “For me, a Parkinson’s diagnosis is not a stop sign but rather a signal that I must make lifestyle changes and dedicate myself to physical therapy in hopes of slowing the disease’s progression.”

He said he would use his voice to help find a cure for the disease. He declined to be interviewed.