What is the most common form of hyperthyroidism, characterized by an autoimmune defect and exophthalmos?

The most common form of hyperthyroidism characterized by an autoimmune defect and the presence of exophthalmos is Graves' disease. This condition arises when the immune system produces antibodies that stimulate the thyroid gland, leading to overproduction of thyroid hormones. One of the hallmark symptoms of Graves' disease is exophthalmos, which is the protrusion of the eyes due to inflammation and swelling of the tissues behind the eyes, often associated with thyrotoxicosis.

The autoimmune nature of Graves' disease is significant; the antibodies typically bind to the thyroid-stimulating hormone (TSH) receptor on thyroid cells, resulting in excessive hormone synthesis and release. This process not only elevates thyroid hormone levels but also can induce symptoms of increased metabolism in various body systems.

The other conditions listed do not fit the description. Hashimoto's thyroiditis is primarily characterized by hypothyroidism due to autoimmune destruction of the thyroid gland, not hyperthyroidism. Subacute thyroiditis usually presents with transient hyperthyroidism due to inflammation but is not classified as autoimmune in the same way as Graves' disease and does not typically involve exophthalmos. Thyroid storm is a life-threatening exacerbation of hyperthyroidism but is not a cause of hyperthyroidism itself