Hashimoto’s Disease: Top 4 Things to Know Furthermore, Graves’ is the most common cause of hyperthyroidism (too much thyroid hormone) in most countries, while Hashimoto’s disease is by far the most common cause of hypothyroidism (too little thyroid hormone production). Both are also the most common causes of thyroiditis, or inflammation of the thyroid gland. These are a result of immune system malfunction and where antibodies against one’s own normal thyroid tissue. Graves’ disease and Hashimoto’s disease are the two most common autoimmune diseases affecting the thyroid gland.
