Endocrinology · Thyroid Disorders
The facts most likely to be tested
Toxic multinodular goiter is caused by autonomous thyroid nodules that function independently of thyroid-stimulating hormone (TSH) regulation.
Patients typically present with subclinical or overt hyperthyroidism in the setting of a palpable, irregular, asymmetric thyroid gland.
The radioactive iodine uptake (RAIU) scan demonstrates a patchy, heterogeneous uptake pattern, distinguishing it from the diffuse uptake of Graves disease.
Plummer disease refers to a specific form of toxic multinodular goiter where a single nodule becomes hyperfunctioning.
Ophthalmopathy and pretibial myxedema are absent in toxic multinodular goiter, helping to clinically differentiate it from Graves disease.
Radioactive iodine ablation or thyroidectomy are the definitive treatments of choice, especially in patients with large goiters or obstructive symptoms.
Methimazole is the preferred thionamide for initial stabilization of hyperthyroid symptoms before definitive therapy.
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A 68-year-old woman presents to the clinic complaining of palpitations, heat intolerance, and a 5-lb weight loss over the last three months. Physical examination reveals a palpable, irregular, asymmetric thyroid gland with multiple nodules. She has no evidence of exophthalmos or pretibial myxedema. Laboratory studies show a suppressed TSH and elevated free T4. A radioactive iodine uptake (RAIU) scan shows patchy, heterogeneous uptake throughout the thyroid gland.
What is the most likely diagnosis?
Toxic multinodular goiter
The combination of a multinodular thyroid, suppressed TSH, and a patchy RAIU scan is pathognomonic for toxic multinodular goiter, distinguishing it from the diffuse uptake seen in Graves disease.
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Etiology / Epidemiology
Common in elderly patients with long-standing iodine deficiency or multinodular goiter.
Clinical Manifestations
Presents as subclinical or overt hyperthyroidism; Plummer disease features a palpable, irregular, asymmetric thyroid gland.
Diagnosis
Radioactive iodine uptake (RAIU) scan shows patchy, irregular uptake in multiple nodules.
Treatment
Methimazole is the preferred antithyroid drug; radioactive iodine ablation is the definitive treatment.
Prognosis
High risk of atrial fibrillation and osteoporosis if left untreated; requires lifelong monitoring.
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Epidemiology & Etiology
Occurs primarily in older adults with a history of non-toxic goiter. It is the second most common cause of hyperthyroidism in iodine-deficient regions. The condition arises from autonomous, TSH-independent functioning of multiple thyroid nodules.
Pertinent Anatomy
The thyroid gland is characterized by multiple nodules of varying sizes. Unlike Graves disease, the gland is typically asymmetric and nodular on palpation rather than diffusely enlarged.
Pathophysiology
Nodules develop autonomous function due to somatic mutations in the TSH receptor gene. These nodules produce excess thyroid hormone, leading to suppressed TSH levels. The surrounding thyroid tissue is typically atrophic due to the lack of TSH stimulation.
Clinical Manifestations
Patients often present with atypical hyperthyroidism, including weight loss, palpitations, and new-onset atrial fibrillation. Unlike Graves disease, patients lack exophthalmos and pretibial myxedema. Thyroid storm is a rare but life-threatening complication triggered by iodine load or stress.
Diagnosis
Initial workup includes TSH (low) and Free T4/T3 (elevated). The Radioactive iodine uptake (RAIU) scan is the diagnostic test of choice, revealing patchy, irregular uptake throughout the gland. This distinguishes it from the diffuse uptake seen in Graves disease.
Treatment
Methimazole is the first-line medical therapy to achieve euthyroidism. Radioactive iodine (RAI) ablation is the definitive treatment of choice for most patients. Surgery (thyroidectomy) is reserved for patients with large goiters causing compressive symptoms like dysphagia or airway obstruction.
Prognosis
Untreated patients face significant morbidity from cardiac arrhythmias and bone density loss. Post-treatment, patients require lifelong monitoring for hypothyroidism, which occurs in a high percentage of patients following RAI ablation.
Differential Diagnosis
Graves disease: diffuse uptake on RAIU and presence of TSH-receptor antibodies
Toxic adenoma: single hot nodule on RAIU with suppressed surrounding tissue
Subacute thyroiditis: painful thyroid and low RAIU due to follicular destruction
Thyroid cancer: cold nodules on RAIU requiring fine-needle aspiration
Exogenous hyperthyroidism: low RAIU and low thyroglobulin levels