Clinical Endocrinology Hyperthyroidism

many as a single entity. The aetiology of the disease remains obscure. It has, however, been clearly established that thyroid-stimulating hormone (TSH) is not responsible for the excessive thyroid activity. An abnormal thyroid stimulator (known as long-acting thyroid stimulator, or LATS), which is both chemically and immunologically distinct from TSH, is found in the serum of many patients with thyrotoxicosis, but its significance is not clear, since in some patients with severe hyperthyroidism LATS cannot be detected. On the present evidence LATS is probably of aetiological importance in some patients. Since LATS is a yG immunoglobulin and reacts with thyroid tissue it has been suggested that thyrotoxicosis, like other thyroid disturbances, may be an autoimmune disease. The role ofLATS in the pathogenesis of thyrotoxicosis has been discussed in two excellent