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Q1: What is the likely diagnosis based on the computed tomogram appearance?
This appearance is highly suggestive of retroperitoneal fibrosis, although sarcoma and lymphoma are also possibilities.
The patient underwent a stenting procedure of the right ureter, which improved the hydronephrosis. She subsequently underwent a ultrasound guided biopsy of the periaortic tissue, and histological examination confirmed fibrotic material with no evidence of malignancy.
Q2: What is the link with the thyroid abnormality?
“Stony hard” or “woody” thyroid enlargement is characteristic of Riedel's thyroiditis. This is a condition characterised by invasion of the thyroid and adjacent structures by a dense fibrosclerotic process. It is a rare cause of hypothyroidism, but a clear association with other sclerotic processes is reported, including idiopathic retroperitoneal fibrosis (see below). As the patient was asymptomatic and not keen to undergo an open biopsy of the thyroid, this procedure was not undertaken. A fine needle aspirate of the thyroid was not attempted as commonly they yield a dry tap in Riedel's thyroiditis. In view of the progressive nature of idiopathic retroperitoneal fibrosis, and its reported response to steroids, a moderate dose of oral prednisolone has recently been started by this patient. Within one month of commencing the steroids, she felt less tired, her goitre reduced in size, and the erythrocyte sedimentation rate fell to 10 mm/hour.
In 1885, Bowlby described a necropsy finding of a hard infiltrative mass around thyroid invading other structures in the neck.1 He presumed this was sarcomatous change within the thyroid with local invasion. Subsequently Riedel described a case of invasive fibrous thyroiditis which he termedRiedel's struma.2 He described the consistency of the swelling as eisenharte strumitis, to emphasise the stony hard or woody nature of the thyroid on palpation. Riedel's thyroiditis is an unusual cause of hypothyroidism and goitre. In a series of 56 000 thyroidectomies from the Mayo Clinic, only 37 were found to have histological evidence of the condition.3 The condition is commonly insidious in onset, and may be asymptomatic.
The association of Riedel's thyroiditis with other fibrotic processes was first described in 1963, when a case of Riedel's thyroiditis was reported in association with retroperitoneal fibrosis, again from the Mayo Clinic.4 Subsequently, around a dozen cases have been reported in the literature, and the concept of a syndrome ofMultifocal fibrosclerosis has been described.5 This comprises multiple fibrotic processes frequently occurring simultaneously in different organ systems. Such conditions include Riedel's thyroiditis, retroperitoneal fibrosis, sclerosing cholangitis, ocular pseudotumour, and mediastinal fibrosis. It is estimated that around 15% of cases of retroperitoneal fibrosis are associated with fibrosis around other structures.6
The pathogenesis of the Riedel's thyroiditis is unclear. An autoimmune aetiology has been hypothesised by the observations of an eosinophilic infiltrate on histological examination, the common presence of thyroid autoantibodies, and frequent association with other autoimmune conditions such as pernicious anaemia, Addison's disease, and hypoparathyroidism. It is of note, however, that the fibrosis seen in Riedel's thyroiditis is commonly not just limited to the thyroid, but also invades other structures within the neck, suggesting a primary fibrotic process starting in the neck, rather than a tissue specific autoimmune condition.
Riedel's thyroiditis is a rare cause of hypothyroidism.
The condition is characterised by the presence of a stony hard or woody thyroid.
15% of cases of retroperitoneal fibrosis are associated with other fibrotic processes such as Riedel's thyroiditis, sclerosing cholangitis, ocular pseudotumour, and mediastinal fibrosis.
Steroids and tamoxifen may be useful in halting the progression of the disease.
More recently, it has been suggested that retroperitoneal fibrosis is an autoallergic reaction to the lipid components of atherosclerotic plaques within the aorta, leading to fibrosis around the aorta. Furthermore, it has been hypothesised that Riedel's thyroiditis may be a periarteritis of the carotid artery resulting in cervical fibrosis subsequently involving the thyroid, and thus the conditions may have a similar pathogenesis, accounting for their common coassociation.7
Treatment of Riedel's thyroiditis and retroperitoneal fibrosis is essentially anecdotal, due to the rarity of the condition. As in our patient, steroids have been used successfully to induce resolution of the fibrotic process in some cases, particularly where compressive complications of the trachea or ureters is present.8 It is of note, however, that spontaneous resolution has also been reported. A further drug that may be of benefit in Riedel's thyroiditis and retroperitoneal fibrosis is tamoxifen, which induces transforming growth factor-β, which is in turn an inhibitor of fibroblast growth factor.9 10
In summary therefore, we present a patient who presented initially with symptomatic hypothyroidism and a hard thyroid swelling compatible with Riedel's thyroiditis, in whom a proved diagnosis of retroperitoneal fibrosis has been made. The co-occurrence of two or more fibrotic processes in different organs is a rare, but well described association, and patients presenting with one such condition may well have evidence of fibrosis elsewhere.
Retroperitoneal fibrosis associated with Riedel's thyroiditis.
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