Graves disease is hyperthyroidism caused by autoantibodies that stimulate the TSH receptor (the receptor for thyroid-stimulating hormone), and its course over time is not a straight line. Some patients with mild Graves disease move between relapse and remission over the course of the illness. Rarely, the balance shifts far enough that hyperthyroidism and hypothyroidism alternate, because the underlying process is autoimmune.
The same autoimmunity can end in hypothyroidism. In some patients the destructive effect of the TSH-receptor antibodies eventually outweighs their stimulating effect, so hypothyroidism appears after years of treatment — in about 15% of patients who enter remission after 10-15 years of therapy.
The eye and skin changes follow their own timelines, which do not track the thyroid hormone level. Ophthalmopathy mainly worsens during the first 3-6 months of the disease and then reaches a plateau over the next 12-18 months. Thyroid dermopathy usually appears 1-2 years after the diagnosis of Graves disease.