The Common Vein Copyright 2010
Definition
Toxic multinodular goiter is an enlarged thyroid gland consisting of several hyperactive thyroid nodules that are autonomously functioning. These “toxic” nodules will produce and release increased amounts of thyroid hormone and are unresponsive to TSH and the negative feedback from increased concentration of thyroid hormones in the blood stream. Left untreated, a toxic nodule and/or toxic multinodular goiter may lead to hyperthyroidism and thyrotoxicosis.
The most common cause of multinodular goiters internationally is iodine deficiency. Decreased levels of iodine cause thyroid hormone deficiency which leads to increased levels of TSH. High levels of TSH cause compensatory hyperplasia of the thyroid gland and formation of hyperplastic nodules. These hyperplastic nodules are at increased risk for somatic genetic mutations that can lead to an autonomously hyperfunctioning nodule.
Structural changes seen are growth of the thyroid gland with palpable or visible nodularity. Functional changes of a toxic nodule are autonomous increased thyroid hormone production. Clinically patients may present with a palpable thyroid nodule or with the sequela of hyperthyroidism. At the extreme of size, tracheal compression can occur do to the anatomical positioning of the thyroid gland.
Imaging of all nodules is important to determine risk of malignancy. Ultrasound may show whether a lesion is solid, cystic, or a combination. Ultrasound has also been found to be useful in determining characteristics of a nodule that are worrisome for thyroid cancer. Thyroid scintigraphy may clearly demonstrate a “hot” nodule which supports the diagnosis of a benign lesion. CT or MRI can be used to evaluate trachea or esophageal compression. Diagnosis is best made with thyroid scintigraphy showing a hyperactive thyroid nodule.
Treatment of toxic nodules depends on the clinical scenario. Patients who are euthyroid may be able to be observed. Patients with overt hyperthyroidism can be treated with medication, radioactive iodine, or surgery.