Sublingual Ectopic Thyroid Presenting with Congenital Hypothyroidism

Introduction

Congenital hypothyroidism (CH) is the most frequent endocrine condition and the most avoidable cause of mental retardation in children [1, 2]. According to available local studies, the prevalence of CH in the country ranges from 1 in 1170 to 3666 live births [2]. Since 1998, all neonates have been screened for CH via the measurement of the cord blood Thyroid Stimulating Hormone (TSH) at birth for early detection and prompt initiation of therapy. Thyroid dysgenesis, observed in as many as 87% of cases, is frequently linked to the underlying etiology of CH [3]. There are three primary categories for this abnormal thyroid gland development: agenesis (15–30%), hypoplasia (5%) and thyroid ectopy (40–60%) [3].We describe here a child with congenital hypothyroidism who was diagnosed with sublingual thyroid ectopy much later in life. The clinical course, diagnosis and management of ectopic thyroid disease are reviewed.

Case Presentation

A 9-year-old boy was referred to pediatric otorhinolaryngology team for throat discomfort. He noticed the symptom for the past 3 months, which were intermittent and associated with frequent throat clearing and production of phlegm. He did not complain of odynophagia, dysphagia, difficulty breathing or snoring during sleep. He had a history of congenital hypothyroidism, which was discovered by an abnormally high cord TSH level of 70.75 mIU/ml at birth. He was put on levothyroxine on day 5 of his life and our pediatric endocrine team continued to monitor him clinically and biochemically after that.

His birth history was unremarkable, he had never undergone surgery or intubation. His developmental milestones were consistently within the typical age range, and he did well in regular schooling. There was no family history of cancer or thyroid conditions. A Technetium-99 m pertechnetate thyroid scintigraphy was performed at the age of 3 years. The sublingual area had abnormal radiotracer uptake, while both the thyroid lobes did not exhibit any uptake, giving the impression of an ectopic sublingual thyroid (Fig. 1). In spite of this, he was well and was under regular follow-up from the pediatric team.

Fig. 1.

99 m-Tc Thyroid Scintigraphy image of anterior view with thyroid cartilage and suprasternal notch marked, revealed a focal area of abnormal radiotracer uptake in the sublingual region with no evidence of radiotracer uptake within both lobes of the thyroid

On physical examination, the child was not syndromic but appeared overweight with a body mass index (BMI) of 25 kg/m². His pulse rate was not tachycardic with a regular rhythm. There was no audible stridor or stertor heard. No palpable neck swelling, or goiter were detected. Intraoral examination revealed no unusual lesion or swelling in the oral cavity or oropharynx. The floor of the mouth was not raised, while the dorsal tongue morphology and movement were normal. Flexible nasopharyngolaryngoscopy showed an enlarged adenoid without any mass or suspicious lesion from the base of the tongue up to the valleculae region. The vocal folds were mobile bilaterally, and the glottis and supraglottis were unremarkable.

The most recent Thyroid Function Test was within the acceptable range. Serum Free T4 was 19.4 (slightly high), while serum Thyroid Stimulating Hormone (TSH) was 2.51 which is normal. He is currently on oral Levothyroxine 50mcg daily (1.2mcg/kg/day). Ultrasound of the neck revealed a homogenous echoic tissue measuring 0.8 × 1.3 cm in the sublingual area, which is most likely the ectopic thyroid (Fig. 2).

Fig. 2.

Ultrasound Thyroid Image showed presence of homogenous echoic tissues at the sublingual area measuring 0.8 × 1.3 cm representing the ectopic thyroid

Interestingly, there were minimal thyroid tissues seen over bilateral thyroid beds that were characterized by multiple cysts, scored as TIRADS 1 (Figs. 3 and 4).

Fig. 3.

Ultrasound thyroid revealed presence of right thyroid lobe measuring 0.9 × 0.9 × 2.0 cm with thyroid cyst seen (white arrow)

Fig. 4.

Left thyroid lobe measuring 0.6 × 0.9 × 2.4 cm seen from ultrasound thyroid performed

He was referred to the dietitian and sports medicine teams for dietary modification and weight reduction, respectively. Upon follow-up 3 months later, he reported improvement in his symptoms with conservative treatment.

Discussions

Ectopic thyroid is the result of interrupted migration of thyroid gland tissue from the foramen caecum to the pretracheal location. The migrating tissue may reside in any location along its course. In as many as 90% of cases, it is located over the base of the tongue (lingual thyroid); sublingual, supra-, or infrahyoid, as well as the mediastinum, are less common locations [4]. It also has a female preponderance, accounting for about 60–80% of cases [4]. The first case of lingual thyroid was described by Hickman in 1869, in which an infant died at sixteen hours of life due to upper airway obstruction [1, 3]. Although lingual thyroid has frequently been described in previous reports, cases of sublingual thyroid remain scarce.

Congenital hypothyroidism is usually treated with levothyroxine and is initiated as soon as a biochemical diagnosis is made to prevent negative developmental sequelae in babies [2]. The underlying etiology of the condition is not usually established prior to the initiation of treatment, as diagnostic imaging is not performed routinely upon diagnosis of CH but rather is done later when there is a clinical indication or during re-evaluation of the thyroid function [2]. Re-evaluation of the thyroid axis is usually done at 3 years of age or older when myelination of the central nervous system has completed [2, 5]. During the evaluation, thyroid hormone supplements are withheld for 4–6 weeks and the child’s thyroid function test is measured. When persistent hypothyroidism is established, the patients are subjected to thyroid ultrasonography or scintigraphy to identify the underlying aetiology [2, 5].

Thyroid scintigraphy using Technetium-99 m pertechnetate is by far the most reliable investigation to underline the cause of CH particularly when thyroid dysgenesis or dyshormogenesis are suspected [2, 5]. The specificity of this test goes up to as high as 100%, as seen in a study done by Keskin et al. It allows visualisation of the location as well as the level of activity of the thyroid tissues. Despite the disadvantages of ionizing radiation exposure in children [5], international guidelines have concluded that thyroid scintigraphy is safe at any age, including newborns [6].

On the other hand, ultrasonography (USG) of the thyroid had a high specificity (100%) but low sensitivity (44%) for the detection of sublingual thyroid [5]. It is an excellent tool to detect anatomical or pathological features of the thyroid gland. However, the drawback lies in its inability to detect most of the thyroid ectopies [4, 5]. Compellingly, a doppler study, when combined with an ultrasound, increases its sensitivity to detect ectopic thyroids [5]. Most studies recommend a combination of both USG and scintigraphy to determine the underlying cause of CH in children, as they complement each other in providing more anatomical and functional information about the disease [2–4]. Nonetheless, considering the effects of ionizing radiation and its cost, Supakul et al. suggested that thyroid scintigraphy may only be needed in selected cases where USG showed equivocal findings. This is because the differentiation between thyroid agenesis and ectopy will not alter management given the fact that thyroid ectopies may eventually regress with TSH suppression [5].

The clinical manifestations of thyroid ectopy largely depend on the location and size of the thyroid tissue [3, 4] They may present with swallowing issues, dyspnea or a palpable mass [3, 4]. A large proportion of the patients are asymptomatic and a diagnosis was only achieved through biochemical and imaging tests [3, 4]. In patients who were already being treated for CH, their thyroid tissues are usually small, attributed to the suppression from the thyroxine supplement [3, 6]. Similarly, our patient remained free of symptoms until the age of nine. Of note, the clinical symptoms will be more apparent during the pubertal period, pregnancy, acute infection or trauma due to hyperactivity of the thyroid gland [6]. In these circumstances, the increase in demand for thyroid hormone causes an increase in TSH levels, leading to the enlargement of thyroid tissue [6].

Therapeutic measures for thyroid ectopia should take into account the size and location of the gland, any presence of local compressive symptoms and the functional status of the thyroid gland [4]. As suggested by Shredder et al. patients who are euthyroid and do not present with obstructive symptoms should be managed conservatively while maintaining levothyroxine therapy, as it may suppress the volume of the gland [3]. Thyroid ablation may be one of the options for treatment, but it is rarely performed, especially in the paediatric population, in view of the high dose of radiation that imposes harm on their growth [6].

Surgical excision of the ectopic thyroid should be reserved in cases where the lesion causes significant airway obstruction, swallowing dysfunction, or is intractable to medical therapy [6–8]. Nevertheless, physicians should be cognizant of the possible sequelae of retaining thyroid tissue at its abnormal site. In the event that the thyroid tissues become inflamed or hyperactive due to the increase in hormonal demand, rapid enlargement and bleeding from the gland may lead to upper airway compromise. Few reports have demonstrated life-threatening upper airway obstruction and intraoral bleeding during puberty and pregnancy [9, 10]. (references) Even though not as common (less than 1% risk) [4], ectopic thyroid tissues were also reported to undergo malignant transformation in sporadic cases in the literature [11].

Conclusion

Sublingual thyroid is a rare cause of thyroid gland dysgenesis. It can be an uncommon cause of CH. Although hormonal supplementation effectively addresses both the negative impacts of co-existing CH and suppresses the growth of the ectopic gland, surgical removal needs to be considered in instances of obstruction to the upper aerodigestive tract, especially during hyperactivity, as well as in the event of malignant transformation.

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed Nur ‘Afeena Al Fahmi Abdul Kashaf, Chee Chean Lim, and Jeyanthi Kulasegarah. The first draft of the manuscript was written by Nur ‘Afeena Al Fahmi Abdul Kashaf and Chee Chean Lim. All authors commented, read and approved the final manuscript.

Funding

No financial support was provided to this work.

Data Availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declarations

Ethical Approval

This is a single case study. The Universiti Malaya Medical Centre Ethics Committee has confirmed that no ethical approval is required.

Consent to Participate

Written informed consent was obtained from the patient’s parent.

Consent to Publish

Patient’s parent signed informed consent regarding publishing patient’s data.

Competing Interests

The authors declare that they have no competing interests.