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.

Signs and symptoms
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

Causes
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.

Diagnosis
Treatments
Toxic multinodular goiter can be treated with antithyroid medications such as propylthiouracil or methimazole, radioactive iodine, or with surgery. Another treatment option is injection of ethanol into the nodules.

History
The usage of terminology for types of goiter has varied over the past century. Physicians and surgeons tend to differentiate among solitary-nodule goiter, multinodular goiter, and non-nodular goiter more thoroughly in recent decades than they formerly did. Thus some sources have described, or still describe, thyroid adenoma (toxic adenoma) as synonymous with toxic multinodular goiter, but other sources differentiate those two as single-nodule disease versus multinodular disease (respectively) with pathogenesis that is likely differing in most cases (e.g., single neoplastic cell clone versus multifocal or diffuse molecular metabolic change). The medical eponyms "Plummer disease" (named after American physician Henry Stanley Plummer) and "Parry disease" (named after English physician Caleb Hillier Parry) have been used to refer to toxic multinodular goiter, toxic adenoma, and toxic diffuse goiter (Graves disease); the specific entity in each patient/case is not always clear retrospectively, especially in older literature. This is logical given that advanced medical imaging that can show what is happening at various places within a thyroid gland inside a living person (such as nuclear medicine imaging of radioiodine tracer uptake) was not available until after the 1940s.

References


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