In 1995, Duffy was diagnosed with a rare form of the disease sarcoidosis called neurosarcoidosis. Her brain and spinal cord were affected, leaving her partially paralyzed. She wrote about her affliction in the humorous 2000 autobiography Model Patient: My Life as an Incurable Wise-Ass. In November 2017 she celebrated the publication of her second book, Backbone: Living with Chronic Pain without Turning into One where she wrote about battling with sarcoidosis for two decades. For Duffy, who can usually only get up three days a week, writing has served as a form of therapy. She hopes that her words will help the many others who also deal with chronic pain.