Toxic Adenoma overview

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Overview

Historical Perspective

Classification

Pathophysiology

Causes

Differentiating Toxic Adenoma from other Diseases

Epidemiology and Demographics

Risk Factors

Screening

Natural History, Complications and Prognosis

Diagnosis

Diagnostic Criteria

History and Symptoms

Physical Examination

Laboratory Findings

Electrocardiogram

X-ray

Echocardiography and Ultrasound

CT scan

MRI

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

Overview

A toxic adenoma is a benign tumor consisting of thyroid follicular cells, which produce excessive amounts of T3 and/or T4. In toxic adenoma, the excessive thyroid hormone autonomously produced can suppress the function of remaining thyroid tissue. Thus thyroid hormone production is no longer controlled by the hypothalamic-hypophyseal-thyroid axis, leading to thyroid hormone excess and the resulting clinical symptoms, signs, and potential complications. The most common cause of toxic adenoma is iodine deficiency. Alteration of the thyroid stimulation pathways by activation of germline or somatic mutations in the TSH receptor or cAMP signal transduction system is believed to be responsible for the development of autonomous thyroid gland growth and hormonogenesis. Patients with toxic adenomas typically present with signs and symptoms of thyrotoxicosis. If left untreated,thyrotoxicosis increases the risks of atrial fibrillation, heart failure, and decreased bone mineral density in [postmenopausal|postmenopausal] women. Measurement of serum TSH is considered as the best initial test in the evaluation of thyroid disorders. The serum free T4 and free or total T3 levels are elevated or in the upper part of the normal range. The mainstay of treatment for most patients with toxic adenoma includes radioiodine, anti thyroid drugs.

Historical Perspective

In 1840, Adolph von Basedow from Germany was the first to coin the term toxic adenoma. In 1913, Henry Plummer was the first to give a detailed description of toxic adenoma.

Classification

Toxic Adenoma can be classified into asymptomatic and symptomatic toxic adenoma based upon the existence of symptoms.

Pathophysiology

Thyroid-stimulating hormone (TSH) binds to its receptor on the surface of thyroid follicular cells. When TSH binds to the TSH receptor, it stimulates adenylyl cyclase conversion of adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP). Activation of this pathway leads to cell growth and thyroid hormone secretion. When TSH concentrations are five- to tenfold higher, TSH binding to its receptor leads to its interaction with Gq, activating phospholipase C, which in turn leads to increased intracellular calcium, diacylglycerol, and inositol phosphate. Activation of this pathway regulates iodination and thyroid hormone production. Alteration of the above pathway by activation of germline or somatic mutations in the TSH receptor or cAMP signal transduction system is believed to be responsible for the development of autonomous thyroid gland growth and hormonogenesis. The molecular alterations responsible for toxic adenomas include somatic gain-of-function mutations in the TSH receptor or the stimulatory Gs alpha subunit. Both result in constitutive activation of the cAMP pathway, which results in enhanced proliferation and function of thyroid follicular cells. Measurement of serum TSH is considered as the best initial test in the evaluation of thyroid disorders. The serum free T4 and free or total T3 levels are elevated or in the upper part of the normal range.

Causes

The most common cause of toxic adenoma is iodine deficiency. Other causes include gene mutations of TSH receptor.

Differentiating ((Page name)) from Other Diseases

Toxic adenoma must be differentiated from other hyperthyroid diseases that cause anxiety, elevated blood pressure and insomnia such as essential hypertension, generalized anxiety disorder, and pheochromocytoma.

Epidemiology and Demographics

The prevalence rates of toxic adenoma is 5-7% and 1-2% of all hyperthyroid cases in women and men respectively. Toxic adenoma is more commonly seen in patients over 60 years. Similar to any thyroid disease females are more commonly affected by toxic adenoma than males. The female-to-male ratio is 5.9:1 for toxic adenoma.

Risk Factors

Common risk factors in the development of toxic adenoma include iodine deficiency, young adult age, head and neck irradiation, family history of thyroid nodules, and female gender

Natural History, Complications, and Prognosis

If left untreated, some of the patients with toxic adenoma may progress to develop thyrotoxicosis which increases the risks of atrial fibrillation, heart failure, and decreased bone mineral density in postmenopausal women. Common complications of toxic adenoma include atrial fibrillation, neck compression, bone mineral loss, thyroid storm, I-131-related hypothyroidism. Prognosis of toxic adenoma is generally good with treatment. About 45% to 75% of patients stay euthyroid following I-131 therapy.

Diagnosis

History and Symptoms

Patients with toxic adenomas typically present with signs and symptoms of thyrotoxicosis. Common symptoms include fatigue, unintentional weight loss, heat intolerance, diaphoresis, palpitations, anxiety, and nervousness. Specific areas of focus when obtaining a history from the patient of toxic adenoma include possibility of recent iodide exposure in any form that can provoke transient thyrotoxicosis in a pre-existing toxic nodule such as medication (e.g., amiodarone), radiocontrast dye, dietary supplements

Physical Examination

Patients with toxic adenoma usually appear fatigued and nervous. Physical examination of patients with toxic adenoma is usually remarkable for widened, palpebral fissures, tachycardia, hyperkinesis, moist, smooth skin, tremor, proximal muscle weakness, and brisk deep tendon reflexes.

Laboratory Findings

Measurement of serum TSH is considered as the best initial test in the evaluation of thyroid disorders. The serum free T 4 and free or total T 3 levels are elevated or in the upper part of the normal range. Findings of routine laboratory tests include elevated serum calcium, elevated alkaline phosphatase, elevated ferritin levels, low (LDL) cholesterol levels.

Electrocardiogram

Electrocardiogram findings of toxic adenoma is mainly due to thyrotoxicosis. Common ECG changes seen with thyrotoxicosis are sinus tachycardia and atrial fibrillation with rapid ventricular response

X-ray

There are no x-ray findings associated with toxic adenom

Ultrasound

Ultrasound is indicated only when adenoma presents as a nonpalpable nodule. Ultrasonography is helpful when correlated with nuclear scans to determine the functionality of nodules. Dominant cold nodules should be considered for fine-needle aspiration biopsy prior to definitive treatment of a TNG.

CT scan

There are no CT findings associated with toxic adenoma.

MRI

There are no MRI findings associated with toxic adenoma.

Other Imaging Findings

Measurement of serum TSH is considered as the best initial test in the evaluation of thyroid disorders. The serum free T 4 and free or total T 3 levels are elevated or in the upper part of the normal range. Radionuclide imaging can be performed with radioactive iodine-123 ( 123 I) or with technetium-99m ( 99m Tc). In patients with hyperthyroidism caused by a toxic adenoma, there is a characteristic restriction of radionuclide uptake to the responsible hyper functioning nodule with suppression of radionuclide uptake in the remainder of the gland.

Other Diagnostic Studies

There are no other diagnostic findings associated with toxic adenoma.

Treatment

Medical Therapy

The mainstay of treatment for most patients with toxic adenoma includes radioiodine, anti thyroid drugs. In patients with overt thyrotoxicosis, beta blocker will alleviate the signs and symptoms mediated by the increased beta-adrenergic activity. Alternative treatment modalities include percutaneous ethanol injection, thermoablation, or radiofrequency ablation. Antithyroid drugs are not routinely employed in the management of toxic adenoma.

Surgery

Subtotal thyroidectomy is the choice of treatment modality for people who decline or are resistant to radioactive iodine. Subtotal thyroidectomy is an effective and prompt treatment for patients with toxic nodular goiter. Reduction of thyroid function is immediate, although recurrent hyperthyroidism or subsequent hypothyroidism is possible. Complications include rare recurrent laryngeal nerve damage and hypoparathyroidism.

Primary Prevention

There are no established measures for the primary prevention of toxic adenoma.

Secondary Prevention

There are no established measures for the secondary prevention of toxic adenoma.

References


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