Autoimmune disease. in some people’s bodies, the
immune system that protects the body from invading
infections can mistake thyroid gland cells and their
enzymes for invaders and can attack them. Then there
aren’t enough thyroid cells and enzymes left to make
enough thyroid hormone. This is more common in
women than men. Autoimmune thyroiditis can begin
suddenly or it can develop slowly over years. The most
common forms are Hashimoto’s thyroiditis and atrophic
thyroiditis.