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Thyroid Canada Newsletter
- Issue 6
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September 2002 Riedel's Thyroiditis Alice YY. Cheng 1, MD,
M. Jean Davidson 2, MD,FRCS(C),
INTRODUCTION Riedel's thyroiditis is a rare fibroinflammatory disease of the thyroid gland. First recognised by Professor Bernhard Riedel in 1883, he published a description in 1896 of two patients with stony hard thyroid swellings causing tracheal compression and invasion into adjacent structures (1). In a review of 56,700 thyroidectomies from 1920-1984 at the Mayo Clinic, only 37 cases of Riedel's thyroiditis were found giving an incidence of only 0.06% (2). An association between Riedel's thyroiditis and other fibrosclerosing lesions, such as retroperitoneal fibrosis, mediastinal fibrosis and sclerosing cholangitis has been reported (3). It has also been associated rarely with tumefactive fibroinflammatory lesions of the head and neck as a part of a broader fibrosclerosing syndrome (4). The exact etiology of the disease remains unclear and the treatment is based on anecdotal reports and case series. We report a case of Riedel's thyroiditis followed by a discussion of the histopathology, clinical features, proposed etiology and treatment of this rare entity.
CASE REPORT A 43 year old woman with a history of recurrent pyelonephritis presented in 1994 with partial nasal obstruction. A 1.5cm x 1.5cm mass could be palpated inferolateral to the left nasal bone on the medial aspect of the face. She was taken to the operating room and the tumour was visualized at the nasal aperture eroding into the medial wall of the maxilla. It was tan in colour and firm. The frozen section examination of the tumour was suggestive of a plasma cell tumour so the mass was removed entirely. Formal microscopic examination revealed fibrous tissue with scattered plasma cell infiltrates and no evidence of malignancy. The final pathologic diagnosis was fibro-inflammatory pseudotumour or tumefactive fibro-inflammatory lesion. Her symptoms resolved post-operatively and the lesion has not recurred. In February 2001, she noted anterior neck pain, fever, fatigue and right flank pain. A diagnosis of right pyelonephritis was made and she was treated with antibiotics. The right flank pain and fever resolved but the neck pain persisted. Soon thereafter, she noticed a firm enlargement on the left side of her neck. She was found to be euthyroid at the time and a 3 cm mass in her left thyroid lobe was noted on ultrasound. The size of the mass increased rapidly and she developed a weak voice, which progressively deteriorated. She also developed difficulty with swallowing and dyspnea when supine. In May 2001, a fine needle aspiration of the thyroid mass was non-diagnostic. She was then referred to a head and neck surgeon. Her left vocal cord had marked decrease in mobility and she had a 7 cm hard, fixed mass in the left lobe of the thyroid gland. She was taken to the operating room where multiple biopsies were sent to pathology for frozen section evaluation and all were negative for malignancy. The hard fibrotic mass had taken over most of the left lobe of the thyroid and was firmly adherent to adjacent structures and invaded the wall of the esophagus, trachea, and both the strap muscles and deep muscles of the neck. The recurrent laryngeal nerve on the left disappeared into the hard fibrotic mass. The planes of dissection were obscured so only the isthmus and half of the left lobe of the thyroid gland superficial to the nerve were removed. The pathological examination of the specimens showed dense fibrous tissue extending into extrathyroidal skeletal muscles. As shown in figure 1, normal thyroid tissue was replaced by a dense sclerotic stroma. Myofibroblasts were seen, surrounded by dense collagen along with prominent lymphoplasmacytic infiltrate composed of small lymphocytes and plasma cells. Prominent venulitis was also present with variable degree of inflammation and sclerosis. The lymphocytes consisted of both B cells and T cells and there was no evidence of neoplasia. A pathologic diagnosis of Riedel's thyroiditis was made. Postoperatively, the patient received tapering doses of corticosteroids for 2 weeks, starting with prednisone 40 mg twice a day, with significant reductions in both the size and firmness of the mass. She also had improvement in voice and resolution of dysphagia and dyspnea. Subsequent CT of her abdomen did not show any evidence of retroperitoneal fibrosis.
Figure 1. Photomicrograph of Riedel’s thyroiditis under low magnification (40X). Dense sclerotic stroma can be seen invading and replacing thyroid follicles in the periphery of the lesion.
To view full size picture click here
DISCUSSION Riedel's thyroiditis is a rare entity and its aggressive nature causes it to be confused with neoplastic processes. Its clinical features are non-specific and a pathologic diagnosis is required. Schwaegerle et al reviewed 185 cases in the English literature and determined certain clinical features of the disease (5). The mean age at time of diagnosis was 47.8 years and 83% were female. Most patients experienced a painless, stony hard, immobile enlargement of a pre-existing goitre. The enlargement can be sufficient to cause significant pressure symptoms including dysphagia and dyspnea. The fibrotic process can involve the recurrent laryngeal nerve and cause vocal cord paralysis and dysphonia. Some patients may experience pain, as in our patient, and this can be referred to the ear or jaw. The fibrotic process can also extend to the parathyroid glands and cause hypoparathyroidism with hypocalcemia (6-9). Riedel's thyroiditis has also been associated with other fibrosclerosing lesions as part of a broader fibrosclerosing syndrome including retroperitoneal fibrosis and mediastinal fibrosis (3,5). Its association with tumefactive fibroinflammatory lesions of the head and neck, as in our patient, is rare and only a few cases have been reported in the English literature (10). The term "tumefactive fibroinflammatory lesion" was first coined by Wold and Weiland to describe an unusual fibrosclerosing disorder of the head and neck that behaved clinically like a malignancy but was histologically benign (5). It is also a rare entity and shares a similar pathology and perhaps, pathophysiology, with Riedel's thyroiditis (5). There have also been reports of associations between Riedel's thyroiditis and pulmonary fibrosis (11), orbital pseudotumours (12,13), renal fibrosis (11), testicular fibrosis (14), pituitary fibrosis (11,14) and parotid fibrosis (15). Comings et al proposed the term "multifocal fibrosclerosis" in 1967 to describe the multi-organ involvement (12). Other labels include "systemic idiopathic fibrosis" and "idiopathic inflammatory fibrosclerosing syndrome". However, only one third of patients with Riedel's thyroiditis will develop extracervical fibrosis within 10 years (7), and only one percent of patients with retroperitoneal fibrosis have Riedel's thyroiditis (8). In the review by Schwaegerle et al, they found that at the time of diagnosis, 64% were euthyroid, 32% were hypothyroid and 4% were hyperthyroid (5). Of those who had thyroid antibodies measured, 67% were positive. An elevated ESR was the only consistent laboratory finding. Ultrasonography of the thyroid mass usually shows a homogeneously hypoechoic mass. CT scan demonstrates hypodense-to-normal thyroid tissue and there is significantly less enhancement with contrast. MRI demonstrates hypointense images on T1- and T2-weighted images and markedly decreased enhancement with gadolinium. In a recent report, Ozgen et al suggested that this may be a diagnostic radiologic finding for Riedel's thyroiditis because no other entity causes diffuse decreased enhancement after iodinated contrast medium or gadolinium administration (16). Despite the clinical features described, Riedel's thyroiditis and tumefactive fibroinflammatory lesions of the head and neck are pathologic diagnoses requiring open surgical biopsy to obtain sufficient tissue (17). Grossly, the lesion is "stony-hard" and well-circumscribed but not encapsulated. There is usually extension of the disease through the capsule and into adjacent structures. It cuts like cartilage and there is no regional lymph node involvement (5). Microscopically, there is an extensive infiltration of lymphocytes, plasma cells, neutrophils and eosinophils. The normal thyroid architecture is effaced. The gland is replaced by dense fibrous tissue and collagen and there is evidence of extension into adjacent structures (5). There is an associated vasculitic process occurring in three stages-infiltrative, occlusive and sclerotic (18). Of note, there are no oxyphilic epithelial cells (Hurthle cells) and there is an absence of granulomatous reaction and absence of neoplasm (5). In 1957, Woolner et al (19) proposed the following criteria for the pathologic diagnosis of Riedel's thyroiditis: 1) fibroinflammatory process involving all or a portion of the thyroid gland; 2) presence of gross and/or histologic evidence of extension into adjacent structures, including strap muscles; 3) fibrotic process causing near-complete destruction of involved portion of the gland. The pathophysiology of the disease remains poorly understood. For a number of years, it was thought that Riedel's thyroiditis merely represented endstage Hashimoto's thyroiditis. However, certain pathological differences between the two makes this hypothesis unlikely. In Riedel's thyroiditis, there is extension beyond the thyroid capsule, effacement of gland architecture and evidence of vasculitis, distinguishing it from Hashimoto's thyroiditis (20). Another proposed etiology is autoimmune. The increased incidence of thyroid antibodies and the few reported associations with type 1 diabetes, Addison's disease and pernicious anemia suggest an autoimmune cause (21). However, no specific autoantibodies or antigen has been identified. In addition, normal serum complement levels and normal lymphocyte subpopulation make this hypothesis less likely (22). The report by Comings et al of two brothers, offspring of a consanguineous marriage, with multifocal fibrosclerosis suggests a genetic factor however, a familial occurrence has only been reported once (12). A vasculitis hypothesis has also been proposed. Vasculitic changes are often seen in cases of Riedel's thyroiditis and other fibrosclerosing lesions such as retroperitoneal fibrosis. Therefore, it has been hypothesised that Riedel's thyroiditis is actually a periarteritis of the carotid resulting in cervical fibrosis with secondary involvement of the thyroid (23). To support this hypothesis, marked tissue eosinophilia and eosinophil degranulation has been noted in the affected parts of the thyroid and perivascular areas (24). This eosinophilia has also been noted in other fibrosclerosing disorders such as retroperitoneal fibrosis, sclerosing cholangitis, sclerosing mediastinitis and pulmonary fibrosis. Eosinophils and its products play a potential role in tissue fibrogenesis (24). However, the primary reason for eosinophil infiltration and degranulation remains unclear. Due to the rarity of this disease, there have been no treatment trials for Riedel's thyroiditis. Surgery is necessary to relieve symptoms of compression such as dysphagia or dyspnea. An extensive resection should not be attempted because tissue planes are obscured and adjacent structures can be damaged (25). Usually, surgery is limited to a wedge resection of the isthmus. In tumefactive fibroinflammatory lesions, surgery may be the first line of treatment if it is technically feasible, otherwise, medical treatment can also be effective (10). Treatment with corticosteroids is the mainstay of
medical therapy for both Riedel's thyroiditis and tumefactive fibroinflammatory
lesions of the head and neck (4,26-28). There have been reports
of dramatic improvements manifested by decreased size of the gland
and softening of the gland with improvement in compressive symptoms
without any surgical intervention (27,28). For some, the benefits
persist even after withdrawal of the steroids (5). Others relapsed,
requiring maintenance steroid treatment and a few had minimal response
to steroids (22). The appropriate dose and duration of treatment
is not well established but most have used high dose steroids (prednisone
80-100mg/day) initially with a slow taper (26-28). In our case,
high dose steroids were quickly tapered off with success. There
is a suggestion that early intervention with steroids is better.
A recent development in the treatment of Riedel's thyroiditis is the use of tamoxifen (25,29). This has not been used to treat tumefactive fibroinflammatory lesions of the head and neck. Few et al reported on four patients with Riedel's thyroiditis of various durations, uncontrolled with surgical treatment and steroids, who had dramatic improvement with tamoxifen 20 mg twice a day (25). The responses were seen within weeks of initiating therapy. The appropriate duration of therapy is unclear. The benefits with tamoxifen are not felt to be due to its anti-estrogen effects. In fact, the benefit is hypothesised to be due to its stimulation of TGF-ß1 secretion (25). TGF-ß1 is a potent growth inhibitor of immature fibroblasts. Therefore, the stimulation of TGF-ß1 would inhibit fibroblasts and stop the fibrotic process (25). This mechanism has been proven definitively. More experience is needed with tamoxifen before recommending it as a mainstay of therapy, however, it would be reasonable to try in patients with this rare entity who fail to respond to surgery and steroids (25). The natural history of the disease is varied. Self-limiting cases have been described along with aggressive, rapidly progressive cases (17). Overall, it is felt that Riedel’s thyroiditis is a benign condition and fatality is rare with isolated Riedel's thyroiditis. Only two fatalities have been reported and these were due to postoperative complications (20). If multifocal fibrosclerosis is present, the prognosis depends on the organ system affected (17). In summary, Riedel’s thyroiditis is a rare, invasive, fibroinflammatory disease of the thyroid gland that may be associated with other fibrosclerosing lesions including tumefactive fibroinflammatory lesions of the head and neck, as in our patient. It is primarily a pathologic diagnosis and its clinical features mimic neoplasm and should be included in the differential diagnosis of a rapidly progressive and invasive thyroid nodule. Its medical treatment includes corticosteroids and tamoxifen. Surgery should only be used to relieve compressive symptoms. Once a diagnosis of Riedel's thyroiditis or tumefactive fibroinflammatory lesion is made, it is important to maintain long-term follow-up and to evaluate for other fibrosclerosing lesions. Although it is often a progressive disease, the prognosis of isolated Riedel's thyroiditis is considered to be quite good.
Alice YY. Cheng 1, MD, M. Jean
Davidson 2, MD, FRCS(C),
Bayardo Perez-Ordonez 3, MD,FRCP(C), Rosario Briones-Urbina 4, MD,Ph.D,FRCP(C)
BIBLIOGRAPHY
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EDITORIAL COMMENT This is the first article submitted by a Resident in Endocrinology & Metabolism which thus may act as a harbinger of things to come. We would welcome further articles from trainees, particularly those of a review nature, which may appeal to our readership in general. Riedel’s Struma is a rare entity involving the thyroid gland, but it is well defined and new studies suggest a relationship to autoimmunity and to eosinophilia which may constitute a fibrogenic product of eosinophils. It will be of considerable interest when the nature of this mysterious entity is clarified. Robert Volpé, MD, FRCP (C), MACP
********* SOURCES OF INFORMATION FOR THYROID CANCER
PATIENTS Cancer Connection, Canadian Cancer Society Thyroid Foundation of Canada ThyCa: Thyroid Cancer The Head & Neck Cancer Foundation Dr. Daniel Drucker The Light of Life Foundation ******** If you would like to see an upcoming thyroid event published in the next issue of Thyroid Canada, please fax the information to Theramed Corporation at (905) 564-4776 as soon as possible. Published with a grant from Theramed Corporation.
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