Hyperthyroidism is classified into two types:
Primary Hyperthyroidism and Secondary Hyperthyroidism
Primary Hyperthyroidism is essentially Graves' disease which accounts for 60-80% of all cases of hyperthyroidism. It is an autoimmune disorder.
Secondary Hyperthyroidism can be due to a nodule, goitre or any rare cause.
Read more about Graves' Disease here
