causes of primary hyperthyroidism
1 In contrast, primary hyperthyroidism occurs when the dysfunction is caused by abnormal functioning of the thyroid gland itself. 2  The condition is very rare in contrast to primary hyperthyroidism, which is fairly common. Secondary Hyperthyroidism indicates that the dysfunction is caused by factors extrinsic to the thyroid gland (i.e., not due to a disorder in the gland). 2  In contrast, primary hyperthyroidism occurs when the dysfunction is caused by abnormal functioning of the thyroid gland itself.