Most autoimmune diseases are not fatal. However, autoimmune diseases are not curable. They are chronic illnesses. Many people with autoimmune conditions that the disease makes them uncomfortable. In fact, it can interfere with the day to day activity of an individual. It can make life unbearable for many.
However, Giant Cell Myocarditis (GCM) is a fatal autoimmune disease. It is a rare type of autoimmune disease where the immune cells cause inflammation of the heart muscles. This can cause chest pain, abnormal heartbeats, heart failure, and, eventually, death.
This rare type of autoimmune disease is common in young and middle-aged adults. It progresses rapidly, as well. Most people with this condition will require a heart transplant at some point.