Toxic multinodular goitre

Toxic multinodular goiter (TMNG), also known as multinodular toxic goiter (MNTG), is an active multinodular goiter associated with hyperthyroidism. It is a common cause of hyperthyroidism in which there is excess production of thyroid hormones from functionally autonomous thyroid nodules, which do not require stimulation from thyroid stimulating hormone (TSH). Toxic multinodular goiter is the second most common cause of hyperthyroidism (after Graves' disease) in the developed world, whereas iodine deficiency is the most common cause of hypothyroidism in developing-world countries where the population is iodine-deficient. (Decreased iodine leads to decreased thyroid hormone.) However, iodine deficiency can cause goiter (thyroid enlargement); within a goitre, nodules can develop. Risk factors for toxic multinodular goiter include individuals over 60 years of age and being female. Symptoms of toxic multinodular goitre are similar to that of hyperthyroidism, including: heat intolerance muscle weakness/wasting hyperactivity fatigue tremor irritability weight loss osteoporosis increased appetite non-painful goitre (swelling of the thyroid gland) tachycardia (high heart rate - above 100 beats per minute at rest in adults) tracheal compression exophthalmos Sequence of events: Iodine deficiency leading to decreased T4 production. Induction of thyroid cell hyperplasia due to low levels of T4. This accounts for the multinodular goitre appearance. Increased replication predisposes to a risk of mutation in the TSH receptor. If the mutated TSH receptor is constitutively active, it would then become 'toxic' and produces excess T3/T4 leading to hyperthyroidism. Hyperthyroidism is diagnosed by evaluating symptoms and physical exam findings, and by conducting laboratory tests to confirm the presence of excess thyroid hormones. It is characterized by high levels of thyroid hormone in the blood along with a low level of thyroid-stimulating hormone (TSH). After diagnosing hyperthyroidism, a thyroid scan can be performed to determine the functionality of the thyroid gland using radioactive iodine.