Introduction
Background
Riedel thyroiditis, or Riedel's thyroiditis (RT), is a rare, chronic inflammatory disease of the thyroid gland characterized by a dense fibrosis that replaces normal thyroid parenchyma. The fibrotic process invades adjacent structures of the neck and extends beyond the thyroid capsule. This feature differentiates RT from other inflammatory or fibrotic disorders of the thyroid. Because of the encroachment beyond the thyroid capsule, other problems can be associated with RT, including hypoparathyroidism, hoarseness (due to recurrent laryngeal involvement), and stridor (due to tracheal compression). Some experts feel that RT is not primarily a thyroid disease but rather that it is a manifestation of the systemic disorder multifocal fibrosclerosis. Approximately one third of RT cases are associated with clinical findings of multifocal fibrosclerosis at the time of diagnosis.
Gross pathology is shown in the image below.
Gross pathology of Riedel's (fibrosing) thyroiditis. The cut edge is avascular, with a characteristic white color. Image courtesy of SL Lee.
In 1883, Professor Bernhard Riedel first recognized the disease. He published a description of 2 cases in 1896 and of a third case in 1897.1 Riedel used the term eisenharte struma to describe the stone-hard consistency of the thyroid gland and its fixation to adjacent structures. He noted the presence of chronic inflammation with fibrosis and the absence of malignancy on microscopic examination. Simple wedge resection of the thyroid isthmus was used to alleviate tracheal obstruction and is still the preferred surgical therapy for RT.
Pathophysiology
The etiology of Riedel's thyroiditis (RT) is unknown. One theory of pathogenesis postulates that RT results from an autoimmune process. A second theory holds RT to be a primary fibrotic disorder.
The following evidence supports an autoimmune pathogenesis for RT:
- The presence of antithyroid antibodies in a significant percentage of patients with RT (67% of 178 cases reviewed in one study)2
- The pathological features of cellular infiltration, including lymphocytes, plasma cells, and histiocytes
- The frequent presence of focal vasculitis on pathologic examination
- The favorable response of a subset of patients with RT to treatment with systemic corticosteroids
However, the presence of normal lymphocyte subpopulations and normal serum complement levels weighs against an autoimmune mechanism. Additionally, elevated levels of antithyroid antibodies may merely reflect the immune system's exposure to sequestered antigens released by the destruction of thyroid parenchyma from a primary fibrotic disorder.
The theory that RT is a primary fibrotic disorder is supported by its association with multifocal fibrosclerosis. This uncommon idiopathic syndrome is characterized by fibrosis involving multiple organ systems. The extracervical manifestations of multifocal fibrosclerosis can include retroperitoneal fibrosis, mediastinal fibrosis, orbital pseudotumor, pulmonary fibrosis, sclerosing cholangitis, lacrimal gland fibrosis, and fibrous parotitis. RT may be but 1 manifestation of this multifocal disease.
The histopathologic changes of RT closely resemble those observed in multifocal fibrosclerosis. Additionally, one third of published RT cases have demonstrated at least 1 manifestation of extracervical fibrosclerosis. The ability of systemic corticosteroids and tamoxifen to inhibit fibrogenesis accounts for the favorable effect of such treatment in both conditions.
Frequency
United States
Riedel's thyroiditis (RT) is a very rare condition. At the Mayo Clinic, 37 cases of RT were diagnosed in a series of 57,000 thyroidectomies performed between 1920-1984, for an incidence of 0.06%. The overall incidence among outpatients was 1.6 cases per 100,000 population. Based on large databases in referral centers, it appears that over the previous decades, the incidence of RT has been decreasing.
Mortality/Morbidity
In Riedel's thyroiditis (RT), morbidity is most frequently related to local compressive symptoms, such as dysphagia, dyspnea, hoarseness, and cough. Hypothyroidism is present in 30% of cases. Fibrotic invasion of adjacent anatomic structures may infrequently result in symptoms related to recurrent laryngeal nerve paralysis or hypoparathyroidism. Death due to airway compromise is very rare in treated patients.
A third of RT patients ultimately develop at least 1 extracervical manifestation of multifocal fibrosclerosis (eg, retroperitoneal fibrosis, mediastinal fibrosis, sclerosing cholangitis).3 In such patients, morbidity and mortality are largely related to the extracervical fibrosclerosis.
Race
Although predominantly reported in whites, Riedel's thyroiditis has been described in all races.
Sex
Riedel's thyroiditis (RT) is most often seen in women. In a review of 178 patients with RT, 83% were women.2
Age
In the above-mentioned series of 178 patients, the mean age at diagnosis of Riedel's thyroiditis was 47.8 years (range, 23-77 y).2
Clinical
History
- Riedel's thyroiditis (RT) is characterized by the replacement of normal thyroid parenchyma with dense fibrotic tissue and by the extension of this fibrosis to adjacent structures of the neck.
- Patients typically present with a hard, fixed, painless goiter. The character of the thyroid gland is often described as stony or woody. The onset of the goiter may be sudden, but it is usually gradual.
- Involvement may be unilateral or bilobar.
- Thyroid function depends on the extent to which the normal thyroid gland has been replaced by fibrotic tissue. Most patients are euthyroid. Hypothyroidism is noted in approximately 30% of cases. Rarely, hyperthyroidism can occur, but this is probably secondary to a coexisting condition.
- Local compressive symptoms, such as neck tightness or pressure, dyspnea, dysphagia, hoarseness, choking, and cough, are frequent. Such symptoms are the result of the increasing thyroid mass or are due to the extension of the fibrotic process to adjacent neck structures (eg, strap muscles, trachea, esophagus, recurrent laryngeal nerve).
- Hypoparathyroidism is rare and presumably reflects fibrotic involvement of the parathyroid glands. Recurrent laryngeal nerve paralysis is also uncommon, but it can be observed in extensive disease.
- Occasionally, spontaneous remission has been reported. Patients can also relapse.
Physical
See History.
- Clinical features of Riedel's thyroiditis (RT) closely resemble those of anaplastic carcinoma of the thyroid. Patients note a nonpainful, rapidly growing thyroid mass. One distinguishing feature of RT is the absence of associated cervical adenopathy. However, accurate diagnosis requires open biopsy.4 RT and anaplastic carcinoma of the thyroid can be distinguished by immunohistochemistry.
- Approximately one third of patients with RT have an associated extracervical manifestation of multifocal fibrosclerosis (eg, retroperitoneal fibrosis, mediastinal fibrosis, orbital pseudotumor, pulmonary fibrosis, sclerosing cholangitis, lacrimal gland fibrosis, fibrosing parotitis).3
Causes
The etiology of Riedel's thyroiditis is unknown.
More on Riedel Thyroiditis |
 Overview: Riedel Thyroiditis |
| Differential Diagnoses & Workup: Riedel Thyroiditis |
| Treatment & Medication: Riedel Thyroiditis |
| Follow-up: Riedel Thyroiditis |
| Multimedia: Riedel Thyroiditis |
| References |
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References
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Further Reading
Keywords
Riedel thyroiditis, Riedel's thyroiditis, thyroiditis, thyroid problems, thyroid disease, hypothyroid, hypothyroidism, Hashimoto's thyroiditis, Hashimoto thyroiditis, chronic sclerosing thyroiditis, chronic fibrous thyroiditis, invasive fibrous thyroiditis, Riedel's disease, Riedel's struma, Riedel disease, Riedel struma, ligneous thyroiditis, ligneous struma, multifocal fibrosclerosis, tracheal compression, thyroid mass, thyroidectomy, corticosteroid therapy
