Riedel's thyroiditis overview

# Overview
Riedel's thyroiditis was first described by Semple, in 1864 and Bolby in 1888. Riedel's thyroiditis was reported to the International Congress of Surgery by Bernhard Riedel in 1894 and 1896. It was initially considered to be the fibrous variant of Hashimoto's thyroiditis but was later recognized as a separate disease. The exact pathogenesis of Riedel's thyroiditis is not fully understood. The presence of thyroid autoantibodies and lymphoid infiltration of the thyroid gland resembling that of Hashimoto's thyroiditis might indicate an autoimmune etiology. It is considered that the infiltrating lymphocytes release cytokines which are responsible for the activation of fibroblasts responsible for the fibrosis. Riedel's thyroiditis is characterized by a replacement of the normal thyroid parenchyma by a dense fibrosis that invades adjacent structures of the neck and extends beyond the thyroid capsule. This makes the thyroid gland stone-hard and fixed to adjacent structures. A shared mechanism with retroperitoneal fibrosis and sclerosing cholangitis has been suggested. Riedel's thyroiditis is considered to have autoimmune etiology and may be caused by the eosinophilia and the proliferation fibroblast as a result of cytokines released by inflammatory cells. Riedel's thyroiditis must be differentiated from other causes of thyroiditis, such as De Quervain's thyroiditis, Hashimoto's thyroiditis, and suppurative thyroiditis. Riedel's thyroiditis is a rare disease with an approximate incidence of 1.06 cases per 100,000 individuals worldwide. Riedel's thyroiditis commonly affects individuals between 30-50 years of age. Females are more commonly affected by Riedel's thyroiditis. Common risk factors in the development of Riedel's thyroiditis include genetic factors, medications such as lysergic acid, ergotamine, serotonin, and other autoimmune diseases such as Graves disease and Hashimoto's thyroiditis. If left untreated, patients with Riedel's thyroiditis may progress to develop complications such as painless neck pressure, hoarseness, stridor, dysphagia, hypothyroidism, hypoparathyroidism, Horner's syndrome, and occlusive phlebitis. Prognosis is generally good and the disease-specific death rate ranges from 6 to 10%. Diagnostic criteria of Riedel's thyroiditis is based on the histopathological findings and includes infiltration of inflammatory cells in the thyroid gland, extension beyond the capsule, evidence of occlusive phlebitis and absence of giant cells, lymphoid follicles, or granulomas. The hallmark of Riedel's thyroiditis is hard and fixed thyroid mass. A positive history of other autoimmune diseases and the use of certain medications is suggestive of Riedel's thyroiditis. The most common symptoms of Riedel's thyroiditis include hard and fixed neck mass, painless goiter, dysphagia, dyspnea, and hoarseness. Less common symptoms of Riedel's thyroiditis include muscular cramps, paresthesias, fatigue, and dry skin. Patients may have the clinical signs of hypocalcemia such as positive Chvostek sign and positive Trousseau sign. Laboratory findings consistent with the diagnosis of Riedel's thyroiditis include elevated ESR, mild elevation of thyroid peroxidase antibodies and occasionally elevated TSH levels. X-ray is helpful to identify esophageal or tracheal compression. CT scan findings suggestive of Riedel's thyroiditis include hypodense infiltrative mass, invasion of nearby soft tissues, compression of the trachea, and esophageal compression. MRI findings suggestive of Riedel's thyroiditis include focal, homogeneous hypointensity in T1 and T2. Ultrasound findings suggestive of Riedel's thyroiditis include hypoechogenicity, thyroid nodule infiltrating adjacent structures, and absence of blood flow on Doppler ultrasound. 24-hour iodine-123 uptake is absent or decreased in Riedel's thyroiditis. Other diagnostic studies for Riedel's thyroiditis include pathological analysis, which demonstrates inflammatory cells infiltration, fibrosis with hyalinization, and extension of fibrosis outside the capsule, and immunohistochemical analysis, which demonstrates the predominance of T lymphocytes, strong positive stain to thyroglobulin, the presence of CD8+, CD4+ and plasma cells. Pharmacologic medical therapies for Riedel's thyroiditis include corticosteroids, tamoxifen, and mycophenolate mofetil. Surgery is usually reserved for patients with esophageal or tracheal compressive symptoms.

# Historical Perspective
Riedel's thyroiditis was first described by Semple, in 1864 and Bolby in 1888. Riedel's thyroiditis was reported to the International Congress of Surgery by Bernhard Riedel in 1894 and 1896. It was initially considered to be the fibrous variant of Hashimoto's thyroiditis but was later recognized as a separate disease.

# Classification
There is no established system for the classification of Riedel's thyroiditis.

# Pathophysiology
The exact pathogenesis of Riedel's thyroiditis is not fully understood. The presence of thyroid autoantibodies and lymphoid infiltration of the thyroid gland resembling that of Hashimoto's thyroiditis might indicate an autoimmune etiology. It is considered that the infiltrating lymphocytes release cytokines which are responsible for the activation of fibroblasts responsible for the fibrosis. Riedel's thyroiditis is characterized by a replacement of the normal thyroid parenchyma by a dense fibrosis that invades adjacent structures of the neck and extends beyond the thyroid capsule. This makes the thyroid gland stone-hard and fixed to adjacent structures. A shared mechanism with retroperitoneal fibrosis and sclerosing cholangitis has been suggested.

# Causes
Riedel's thyroiditis is considered to have autoimmune etiology and may be caused by the eosinophilia and the proliferation fibroblast as a result of cytokines released by inflammatory cells. Although some drugs such as methysergide, serotonin, lysergic acid, and ergotamine have also been identified as the cause of retroperitoneal fibrosis, there are no reports of the direct association with Riedel's thyroiditis.

# Differentiating Riedel's thyroiditis from Other Diseases
Riedel's thyroiditis must be differentiated from other causes of thyroiditis, such as De Quervain's thyroiditis, Hashimoto's thyroiditis, and suppurative thyroiditis.

# Epidemiology and Demographics
Riedel's thyroiditis is a rare disease with an approximate incidence of 1.06 cases per 100,000 individuals worldwide. Riedel's thyroiditis commonly affects individuals between 30-50 years of age. Females are more commonly affected by Riedel's thyroiditis.

# Risk Factors
Common risk factors in the development of Riedel's thyroiditis include genetic factors, medications such as lysergic acid, ergotamine, serotonin, and other autoimmune diseases such as Graves disease and Hashimoto's thyroiditis.

# Screening
There is insufficient evidence to recommend routine screening for Riedel's thyroiditis.

# Natural History, Complications, and Prognosis
If left untreated, patients with Riedel's thyroiditis may progress to develop complications such as painless neck pressure out of proportion to the size of the goiter, hoarseness, stridor, dysphagia, hypothyroidism, hypoparathyroidism, Horner's syndrome, and occlusive phlebitis. Prognosis is generally good and the disease-specific death rate ranges in frequency from 6-10% in the patients with Riedel's thyroiditis.

# Diagnosis

## Diagnostic Criteria
Diagnostic criteria of Riedel's thyroiditis is based on the histopathological findings and includes infiltration of inflammatory cells in the thyroid gland, extension beyond the capsule, evidence of occlusive phlebitis and absence of giant cells, lymphoid follicles, or granulomas.

## History and Symptoms
The hallmark of Riedel's thyroiditis is hard and fixed thyroid mass. A positive history of other autoimmune diseases and the use of certain medications is suggestive of Riedel's thyroiditis. The most common symptoms of Riedel's thyroiditis include hard and fixed neck mass, painless goiter, dysphagia, dyspnea, and hoarseness. Less common symptoms of Riedel's thyroiditis include muscular cramps, paresthesias, fatigue, and dry skin.

## Physical Examination
Physical examination of patients with Riedel's thyroiditis is usually remarkable for hard thyroid mass and clinical signs of hypothyroidism such as fatigue, bradycardia, bradypnea. Patients may have the clinical signs of hypocalcemia such as positive Chvostek sign and positive Trousseau sign.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of Riedel's thyroiditis include elevated ESR, mild elevation of thyroid peroxidase antibodies and occasionally elevated TSH levels.

## Electrocardiogram
There are no ECG findings associated with Riedel's thyroiditis.

## X-ray
X-ray findings in Riedel's thyroiditis are helpful to identify esophageal or tracheal compression.

## CT scan
CT scan may be helpful in the diagnosis of Riedel's thyroiditis. Findings on CT scan suggestive of Riedel's thyroiditis include hypodense infiltrative mass, invasion of nearby soft tissues, compression of the trachea, and esophageal compression.

## MRI
MRI may be helpful in the diagnosis of Riedel's thyroiditis. Findings on MRI suggestive of Riedel's thyroiditis include focal, homogeneous hypointensity in T1 and T2.

## Ultrasound
Ultrasound may be helpful in the diagnosis of Riedel's thyroiditis. Findings on an ultrasound suggestive of Riedel's thyroiditis include hypoechogenicity, thyroid nodule infiltrating adjacent structures, and absence of blood flow on Doppler ultrasound.

## Other Imaging Findings
24-hour iodine-123 uptake is absent or decreased in Riedel's thyroiditis.

## Other Diagnostic Studies
Other diagnostic studies for Riedel's thyroiditis include pathological analysis, which demonstrates inflammatory cells infiltration, fibrosis with hyalinization, and extension of fibrosis outside the capsule, and immunohistochemical analysis, which demonstrates the predominance of T lymphocytes, strong positive stain to thyroglobulin, the presence of CD8+, CD4+ and plasma cells.

# Treatment

## Medical Therapy
Pharmacologic medical therapies for Riedel's thyroiditis include corticosteroids, tamoxifen, and mycophenolate mofetil.

## Surgery
Surgery is usually reserved for patients with esophageal or tracheal compressive symptoms.

## Primary Prevention
There are no established measures for the primary prevention of Riedel's thyroiditis.

## Secondary Prevention
There are no established measures for the secondary prevention of Riedel's thyroiditis.