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The hallmark of Pendred syndrome is the combination of sensorineural deafness and goiter in the presence of a positive perchlorate discharge test. The clinical manifestations of this syndrome can be highly variable between affected families and even within the same family [5].

The true incidence of the syndrome is not known, and depends in part on whether it is defined on a purely clinical basis, or on a genetic basis. The incidence of congenital deafness has been reported to be between 1:1,000 and 1:2,000, and 1-8% of patients with congenital hearing loss are thought to have Pendred syndrome [6, 7]. This suggests that the incidence of Pendred syndrome may range from 1:12,500 to 1:200,000. However, this estimate is based on data collected long before the genetic etiology of Pendred syndrome was known. New studies are needed to determine what percentage of patients with congenital hearing loss have mutations in the PDS gene, and what percentage of these have complete syndrome (see below).

Most patients with Pendred syndrome are born with severe to profound bilateral sensorineural hearing loss, although some appear to have normal hearing initially and lose their hearing suddenly or gradually later in childhood or adolescence.

In contrast, the thyroid disease associated with Pendred syndrome rarely presents in infancy, usually appearing in late childhood or early adolescence as diffuse or multinodular goiter. Typically, the patients are clinically euthyroid, although mild, compensated hypothyroidism, characterized by elevated TSH with normal thyroxin and tri-iodothyronine levels, is often present. However, clinical presentation is variable and Massa et al. recently described a case of documented Pendred syndrome in whom the presenting thyroid pathology was a painless, benign solitary thyroid nodule that resolved after hormone replacement [8]. The size of the goiter is also variable, and may be small, detectable only on close physical examination, or may reach massive proportions, causing significant cosmetic problems or even tracheal compression (fig. 1) [9]. Although the goiter tends to recur after surgery, partial thyroidectomy may be required. The histological appearance of the thyroid tissue is characterized by hyperplastic, diffuse goiter that develops into a multinodular pattern later in life [10] (fig. 2). Frank hypothyroidism can occur after thyroidectomy, presumably due to acute loss of thyroid mass, and full hormone replacement is advised regardless of the extent of the surgical resection. The incidence and severity of the goiter may be related in part to iodine intake, and high levels of dietary iodine intake, such as typically seen in Japan, may protect against the goiter [11, 12].

Patients with Pendred syndrome typically have elevated or high-normal TSH levels in the setting of normal or low-normal levels of T4, with high T3/T4 ratios (fig. 3) [3]. Thyroglobulin levels are frequently elevated and may be extremely high. However, the laboratory findings are of minor clinical significance since there is considerable overlap between patients and unaffected individuals. Furthermore, elevated TG levels are not specific and can be found in MNG from any cause [9]. Although association has been made between the

Fig. 1. CT of neck of Pendred syndrome patient with large multinodular goiter. In this case, the goiter is symmetrical and does not cause any significant displacement or constriction of the trachea. In some cases, critical tracheal compression may occur and thyroidectomy may be required to prevent upper airway obstruction.

Fig. 1. CT of neck of Pendred syndrome patient with large multinodular goiter. In this case, the goiter is symmetrical and does not cause any significant displacement or constriction of the trachea. In some cases, critical tracheal compression may occur and thyroidectomy may be required to prevent upper airway obstruction.

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Fig. 2. The histological appearance of thyroid tissue from a patient with Pendred syndrome and multinodular goiter. HE staining showing thyroid nodules surrounded by fibrous capsules of different shapes and sizes as well as marked hyperplasia of the follicular epithelial cells. The wide variability in size and shape of the colloid follicles is also demonstrated.

Fig. 2. The histological appearance of thyroid tissue from a patient with Pendred syndrome and multinodular goiter. HE staining showing thyroid nodules surrounded by fibrous capsules of different shapes and sizes as well as marked hyperplasia of the follicular epithelial cells. The wide variability in size and shape of the colloid follicles is also demonstrated.

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