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An Interesting Case of Thyrotoxicosis
Address for correspondence: Dr. Subramanian Kannan, Department of Endocrinology, Mazumdar Shaw Medical Centre, Narayana Hrudayalaya Hospitals, Bengaluru, Karnataka, India. E-mail: subramanian.kannan@gmail.com
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Abstract
Ectopic thyroid tissue can be present in the embryonal path of descent of the thyroglossal duct anywhere from the foramen caecum to the thyroid gland. However, for such ectopic thyroid tissue to be hyperfunctioning is quite rare. Here, we discuss a 56-year-old female patient who presented with persistent thyrotoxicosis for over 7 years. She had undergone thyroidectomy in 1982 for thyrotoxicosis and was rendered hypothyroid (thyroid-stimulating hormone of 75 μIU/mL). Whole-body technetium scan was done twice which did not show any uptake in the neck or other parts of the body and an empirical dose of 15 mCi of radioiodine therapy was also given to treat the thyrotoxicosis. She continued to be thyrotoxic and was on carbimazole 30 mg/day along with beta-blockers. In 2021, an Iodine131 whole-body scan revealed small remnant thyroid tissue and an ectopic thyroid tissue in a thyroglossal cyst. In such cases of persistent or recurrent thyrotoxicosis despite standard treatments, an ectopic location should be sought after and treated.
Keywords
Ectopic thyroid
iodine 131 scan
posttotal thyroidectomy
technetium-99m-pertechnetate-whole body scan
thyroglossal cyst
thyrotoxicosis
Case History
A 56-year-old female was referred by cardiologist for palpitations and uncontrolled thyrotoxicosis. She was diagnosed with thyrotoxicosis in the past and total thyroidectomy was performed in 1982. Postsurgery, she was documented to be hypothyroid with a thyroid-stimulating hormone (TSH) of 75 μIU/mL (reference range: nonpregnant – 0.465–4.68 μIU/mL) and she was on daily dose of 100 mcg of L-thyroxine which was later reduced to 75 mcg. Patient had undergone hysterectomy and bilateral oophorectomy in 2001. Since 2015, she developed signs and symptoms of thyrotoxicosis (TSH –<0.01 μIU/mL, free T4 –2.8 ng/dl [reference range: 0.78–2.19 ng/dl], and free T3 – 4.12 pg/ml [reference range: 2.77-5.27 pg/ml]) even after completely stopping L-thyroxine. Due to persistent thyrotoxicosis, she underwent a Technetium-99m pertechnetate (Tc99m) neck scan which showed no uptake and an empirical ablation with 15 mCi radioiodine was done in 2016. Since she was persistently thyrotoxic, she remained on varying doses of tablet carbimazole (20–40 mg), but she was noncompliant to the medication. A summary of the thyroid function tests is shown in Table 1.
| Date | Heart rate (beats/min) | TSH (µIU/ml) | T4 (mcg/dl)/free T4 (ng/dl) | T3 (ng/dl)/free T3 (pg/ml) | Dose of carbimazole/day (mg) |
|---|---|---|---|---|---|
| July 31, 2018 | 100 | <0.01 | T4 (28) | T3 (412) | 20 |
| June 25, 2019 | 99 | 0.002 | T4 (>30) | T3 (519) | 30 |
| October 14, 2019 | <0.0025 | 40 | |||
| November 22, 2019 | 91 | 0.012 | T4 (>30) | T3 (397) | 40 |
| December 21, 2020 | <0.015 | fT4 (2.77) | fT3 (5.53) | 20 | |
| June 27, 2021 | <0.015 | fT (4.7) | fT3 (>22.8) | Off medicine | |
| March 16, 2022 | <0.010 | fT4 (4.06) | fT3 (6.26) | 30 | |
| May 12, 2022 | 88 | 0.7 | fT4 (1.9) | fT3 (4.26) | 30 |
Reference ranges: TSH-nonpregnant: 0.465-4.68 μIU/mL, total T4: 5-12 mcg/dl, free T4: 0.78-2.19 ng/dl, total T3: 71-180 ng/dl, free T3: 2.77-5.27 pg/ml. TSH: Thyroidstimulating hormone, fT4: Free thyroxine, fT3: Free triiodothyronine
When she presented to our center with thyrotoxicosis, a whole-body Tc99m with proper prescan preparation (no recent administration of iodine-containing medications/levothyroxine supplementations) showed no uptake [Figure 1a and b]. Her serum thyroglobulin was 3.27 ng/ml (reference range: 3.5–77 ng/ml), antithyroglobulin antibody was 20.79 IU/ml (reference range: <115 IU/ml), and TSH receptor antibody was 0.96 IU/L (reference range < or = 1.22 IU/L). Neck ultrasound on the thyroid bed showed a small 3.2 mm × 4.2 mm thyroid bed remnant on the right side. We then performed a whole-body Iodine131 scan which showed focus of tracer uptake in the anterior neck, likely thyroid remnant and another focus of uptake in the neck superior to the previous focus, likely a thyroglossal duct remnant [Figure 1c and d]. Repeat ultrasonography of the neck was done including the area above and below the hyoid bone and level I area which showed a small residual gland in the right thyroid bed, size 3.2 mm × 4.2 mm and 19.8 mm × 8.8 mm thyroglossal cyst over the left side below the hyoid bone with solid echogenic material within the cyst [Figure 1e and f]. She was given the options of surgical removal or repeat ablation with a higher dose (30 mCi) of radioiodine but she opted to be on antithyroid medications at present. She is currently euthyroid on a daily dose of 30 mg carbimazole.
Discussion
In thyrotoxicosis, the usual treatment modalities are antithyroid medications, radioiodine ablation, and surgical removal of the thyroid gland.[1] Although rare, the recurrence of thyrotoxicosis after total thyroidectomy can be seen due to remaining thyroid tissue or ectopic functional thyroid tissue or overtreatment with thyroxine supplement.[2] Ectopic thyroid tissue can be found anywhere between the foramen cecum and the normal position of the thyroid gland, the structure connecting both is the thyroglossal duct which normally atrophies before the formation of definitive thyroid gland. It can be present in other sites also such as mediastinum, lung, trachea, duodenum, pancreas, adrenals, and heart. The prevalence of ectopic thyroid tissue is about 1 per 100,000–300,000 people, rising to 1 per 4000–8000 patients with thyroid disease.[34] The presence of ectopic thyroid tissue is due to improper migration during the developmental process along the thyroglossal duct. Posttotal thyroidectomy the ectopic thyroid tissue within the thyroglossal duct remnant, rarely, can produce persistent or recurrent thyrotoxicosis.[24] The reason can be due to overfunctioning thyroid tissue within the thyroglossal duct remnant[2] and failure of a single dose of Radioactive iodine ablation (RAIA) (up to 7% failure rate as reported in the literature).[5] In our case, the remnant and ectopic gland were not picked up by the first technetium scan as there is only uptake of technetium and no organification, it is possible that the retention from the remnant and the ectopic location was not captured due to rapid wash out of the technetium tracer as compared to the trapping, organification, and long half-life of Iodine131. Here, ultrasound can plays an important role if the entire embryological pathway of the thyroid is assessed in case of a negative technetium scan so as not to miss an ectopic source of hormone hypersecretion.
In case of persistent or recurrent thyrotoxicosis despite standard treatments, an ectopic location particularly along the thyroglossal duct tract should be sought after and treated.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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