Point out that hyperthyroidism's exact cause is unknown. Explain to the patient that the condition has four main forms: Graves disease is the most common, and may be related to an immune defect that causes formation of abnormal antibodies. It may follow an emotional shock, stress, or infection. In toxic nodular goiter, one or more thyroid nodules become hyperproductive. This condition is more common in older women with preexisting goiter. Autoimmune thyroiditis(Hashimoto's disease) may cause initial hyperthyroidism before developing into hypothyroidism. Factitious hyperthyroidism results from excessive amounts of thyroid hormone medications.