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By Ashleigh Elkins

Background

A thyroglossal duct cyst is a congenital abnormality that results from a persistent thyroglossal duct. Thyroglossal cysts present as a neck swelling, generally in the midline or slightly to one side. They are generally smooth and painless. However, thyroglossal cysts are prone to infection and an infected cyst will often be quite painful.[1] Some patients may also experience other symptoms related to the cyst, including dysphagia and hoarseness.[2] Approximately 2/3 of patients with thyroglossal cysts have ectopic thyroid tissue within the cyst.[1]

Upon physical examination, a thyroglossal cyst can be differentiated from other neck lumps by observing the movement of the cyst/lump when the patient is swallowing or protruding their tongue. If the lump is a thyroglossal cyst, it will move upwards with swallowing or tongue protrusion.[1] The majority of thyroglossal cysts are detected during childhood. The location of a thyroglossal duct cyst can vary. Some are located above the hyoid bone, others are between the hyoid bone and thyroid cartilage and others are below the sternum. Cysts may also occur within the tongue.[2] The majority of thyroglossal cysts are located below the level of the hyoid bone, with approximately 60-80% of thyroglossal cysts being infrahyoid.[1]

Embryology

The thyroid gland initially develops on the base of the tongue and migrates to its final anatomical position during later stages of development. At approximately gestational week four, the foramen cecum develops as a result of an invagination of the pharyngeal membrane. The primitive thyroid originates from the foramen cecum, and descends into the neck via the thyroglossal duct, a tract running from the base of the tongue to the neck. After the thyroid cells have migrated, the thyroglossal duct regresses at approximately week 10. However, in some people, the thyroglossal duct does not regress completely, and parts of or the entire duct remains, giving rise to a thyroglossal cyst.[2]

Patients routinely undergo ultrasound studies prior to undergoing the Sistrunk procedure to determine whether there is a normally functioning thyroid gland in its anatomical position. Thyroid function tests are generally also ordered pre-operatively to determine whether or not the patient is euthyroid. If the patient does not have a functioning thyroid gland, then surgery is not usually performed, in order to minimise the risk of developing hypothyroidism.

Surgical procedure

Thyroglossal cysts are managed by surgical removal. Surgical removal of the thyroglossal cyst is indicated because the cysts are prone to infection, and for cosmetic and aesthetic reasons. In rare instances, thyroglossal cysts may be malignant. This is thought to occur in less than 1% of all cases, and the underlying malignancy is usually papillary thyroid cancer.[2] Thyroglossal cysts are removed by a surgical procedure called the Sistrunk procedure. This operation is named for the surgeon who first described it. Prior to the development of the Sistrunk procedure, thyroglossal cysts were treated merely by incision and drainage, with recurrence being a key issue.

Due to the problems with recurrences, there was a move towards removing the cyst, along with part of the hyoid bone above it. Recurrence rates were lower with this type of operation compared to incision and drainage, but were still quite high. In 1920, Walter Sistrunk described an extended version of the previous operation. The Sistrunk procedure involved removing the cyst and part of the hyoid bone, as well as removing a small core of tissue from the hyoid bone all the way to the foramen cecum, resulting in a much lower rate of recurrence.[1]

How the Sistrunk Procedure is Performed

  1. A transverse incision is made along the neck is made at the level of the hyoid bone. The incision is approximately 5cm in length.
  2. The skin and the platysma muscle are reflected to expose the cyst, which is commonly found underneath the raphe which connects the sternohyoid muscles
  3. The cyst is then dissected away from the surrounding muscles and tissues up to the level of the hyoid bone
  4. At the hyoid bone, the muscles which attach to the centre of the bone are resected and separated, and then a section of the centre of the hyoid about 2cm is removed together with the cyst and tract.
  5. From the superior aspect of the hyoid bone up to the level of the foramen cecum, a core of tissue is then removed as needed. The diameter of the core of tissue surrounding the thyroglossal duct is approximately 1cm.
  6. In the original Sistrunk procedure the foramen cecum was removed, along with part of each genioglossus muscle and the raphe joining the mylohyoid muscles are also removed. This is now only performed as needed depending on the location of the cyst and path of the thyroglossal tract.
  7. If the tract extended to the tongue base and needed to be removed the opening into the mouth would be closed. Then the genioglossus muscles are sutured, and the tissues at the cut ends of the hyoid bone drawn together with sutures.
  8. A drain is inserted near the hyoid bone and the skin is closed over it.[3]

Extended Sistrunk Procedure

There are two main limitations of the Sistrunk procedure. Firstly, the procedure does not aim to resect the portion of the thyroglossal duct that lies below the hyoid bone. Secondly, the thyroglossal duct is not a simple, straight tube-like structure. It is often a tortuous structure, particularly between the tongue base and the hyoid bone. In some sections the duct may be incomplete. Furthermore, the duct has several side branches, which may not be resected by the standard Sistrunk procedure. Because the procedure originally described by Sistrunk may not result in complete resection of the entire thyroglossal duct, an extended Sistrunk procedure has been described which aims to surgically remove the entire thyroglossal duct.[4]

For the extended Sistrunk procedure, the skin incision is made lower, usually at the level of the thyroid isthmus. The site of the incision may vary if there are any neck swellings or fistulae that will also need to be resected. Starting at the superior aspect of the thyroid isthmus, a section of tissue which includes both the thyroglossal duct and part of the bordering strap muscles is dissected. The resection continues superiorly towards the hyoid bone, removing the thyroglossal duct and cyst. As with the original Sistrunk procedure, a section of the hyoid bone is removed in the extended procedure. Above the level of the hyoid, the thyroglossal duct and cyst are resected along with a wider core of normal tissue, to ensure that any branches of the thyroglossal duct are also removed. This resection continues until the level of the tongue base; however, the tongue base is ideally not breached by the surgeon. A drain is placed in the neck at the end of the procedure and the wound is closed.[4]

Complications

As with all surgical procedures, there are potential risks and complications associated with both the standard Sistrunk procedure and the extended Sistrunk procedure. Major complications associated with the Sistrunk procedure are rare. Potential major complications include nerve injury, airway injury, thyroglossal cyst recurrence, hypothyroidism, blood transfusion and the development of a haematoma or abscess which may require further surgical intervention.[5]

Minor complications are more common than major complications after surgery. Minor complications are usually related to the wound, including superficial surgical site infections, small abscesses around the sutures, seromas and dehiscence of the wound. These minor complications are associated with very low morbidity and can be easily managed in an outpatient setting.[5]

The risk of developing major complications following the Sistrunk procedure is low for several reasons. The placement of a drain helps to reduce the risk of developing a haematoma and aseptic technique and antibiotic prophylaxis minimises the risk of infection. Furthermore, risk of injury to the airway and major vessels and nerves of the neck can be minimised by employing a meticulous surgical technique and by identifying key anatomical landmarks in order to reduce the risk of inadvertent injury to surrounding structures.[5]

Recurrence

Reported recurrence rates following the Sistrunk procedure are low, between 0 and 8%. In comparison, recurrence rates following incision and drainage of thyroglossal cysts exceeded 50%.[1] One study which has described the use of the extended Sistrunk procedure for primary excision of thyroglossal duct cyst reported a 0% recurrence rate at 3 years follow-up. When the extended Sistrunk procedure is implemented in revision cases, the recurrence rate is 7%.[4]

For more information about thyroglossal duct cyst and Sistrunk procedure click here.

References

[1] Wagner G, Medina JE. Excision of thyroglossal duct cyst: the Sistrunk procedure. Operative Techniques in Otolaryngology (2004); 15: 220-223

[2] Goldsztein H, Khan A, Pereira KD. Thyroglossal duct cyst excision—The Sistrunk procedure. Operative Techniques in Otolaryngology (2009); 20: 256-259.

[3] Sistrunk WE. The surgical treatment of cysts of the thyroglossal duct. Annals of Surgery (1920); 71:121-124.

[4] Ahmed J, Leong A, Jonas N, Grainger J, Hartley B. The extended Sistrunk procedure for the management of thyroglossal duct cysts in children: how we do it. Clinical Otolaryngology (2011); 36:252-279.

[5] Maddalozzo J, Venkatesan TK, Gupta P. Complications associated with the Sistrunk procedure. The Laryngoscope (2001); 111: 119-123.

The post Sistrunk Procedure for Thyroglossal Duct Cyst appeared first on Thyroid Clinic Sydney.

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By Ashleigh Elkins

Thyroidectomy is a commonly performed surgical procedure which involves the removal of the thyroid gland. Historically, thyroidectomy has been performed as an open procedure with an incision in the anterior neck, which is usually longer than 6 centimetres.

The open procedure provides the surgeon with good visualisation and exposure of the thyroid gland and surrounding structures, such as the recurrent laryngeal nerve and the parathyroid glands.[1] Open thyroidectomy carries a low complication rate and is regarded as a safe procedure.[2] A disadvantage of open thyroidectomy is scar formation post-operatively. The incision is made in the lower, anterior neck. This area is not typically covered by clothing and is visible to others, and patients may be dissatisfied with the scarring.[1] The incision is typically made into one of the creases into the lower neck, and with good post-operative wound care and taping, the wound usually settles sufficiently to blend in with the creases of the skin. Open thyroidectomy also requires more dissection of neck tissues, which can contribute to post-operative pain.

Minimally Invasive Techniques

In order to improve cosmetic outcomes post-surgery, post-operative pain and duration of hospital stay, minimally invasive thyroidectomy techniques have been developed. These procedures typically utilise endoscopy or video assistance and involve smaller incisions than the open procedure.[2,3] Some endoscopic techniques involve making no incisions into the neck. Instead, the thyroid is approached via incisions made into the axilla, chest or breast. This ensures that the post-operative scars are less visible than those made in the neck. However, a disadvantage of these approaches is that they involve a substantial degree of tissue resection in sites distant from the thyroid gland. Although they may achieve superior cosmetic outcomes, they may not be minimally invasive from a tissue resection point of view.[1]

As there are no cavities in the neck, the amount of space available for the surgeon to work within is limited. Hence, endoscopic thyroid surgery requires the creation of a working space within the neck, which can be achieved by carbon dioxide insufflation, where carbon dioxide is blown into the neck to create a working space. This is a technique commonly used in endoscopic abdominal surgery. Potential complications include elevated blood levels of carbon dioxide and subcutaneous emphysema.[3]  Another technique which has been devised to increase the working space within the neck is known as anterior skin lifting, in which the skin is pulled upwards and away from the body.[3]

Incision Lengths

In minimally invasive video assisted thyroidectomy, an incision is made into the neck that is approximately 2 centimetres in length. This incision is made either to one side of the thyroid gland, or slightly above the sternal notch. In comparison, traditional open thyroidectomy is performed through an incision into the base of the neck, which is generally around 6cm to 10cm in length, depending on the size of the neck and the thyroid gland.[1]

However, depending on the underlying pathology and size of the thyroid gland to be removed, open thyroidectomy may be possible through a smaller incision.[4] The length of incisions made into the chest, axilla and breast vary. These are usually small incisions and due to their position, are usually covered by clothing.[3] For patients undergoing a hemithyroidectomy procedure, which removes one lobe of the thyroid gland, the neck incision is usually smaller, at around 4cm to 5cm.

Who is Eligible for Minimally Invasive Thyroid Surgery?

One of the issues with minimally invasive thyroid surgery is that not all patients are eligible for the procedure. Generally speaking, patients are considered to be eligible for minimally invasive thyroid surgery if they have small thyroid nodules (that is, the largest diameter of the nodule is less than 30mm), the volume of the thyroid gland is less than 20mL (this is usually determined by ultrasound), if they have not had any previous neck surgery or radiation treatments to the neck, and if the patient does not have thyroiditis.[5] Patients with malignancies are generally treated with an open thyroidectomy procedure. Patients who are best suited to undergoing minimally invasive thyroid surgery have small nodules which are located within normal sized or slightly enlarged thyroid glands.

Reported Outcomes of Minimally Invasive Thyroid Surgery

Open thyroidectomy is a safe procedure with a low complication rate and results in good patient outcomes. The main issue with the open procedure is that sometimes patients are not satisfied with the appearance of the scar. Minimally invasive thyroid surgery was developed to reduce the size of the neck scar. The results of minimally invasive thyroid surgery have been promising in patients who have been carefully selected and are appropriate candidates for the minimally invasive surgery. Patients who have been selected for the minimally invasive surgery, but are not suitable for the procedure (usually because their thyroid gland is too large), will have their operation converted to an open procedure to ensure the best results are obtained.

Patients undergoing the minimally invasive procedure are generally observed overnight in hospital in case of complications. This is also standard for many patients who undergo the open procedure. Complication rates, including post-operative bleeding, recurrent laryngeal nerve palsy, and hypocalcaemia following minimally invasive thyroid are comparable to the open procedure. Minimally invasive techniques may be associated with a better cosmetic outcome and less pain post-surgery.

Advantages of Minimally Invasive Thyroid Surgery

Minimally invasive thyroid surgery is generally performed in young, fit women who have few skin creases in the neck, who meet the above selection criteria. This is because the minimally invasive technique produces a smaller, less visible scar than the open procedure.

Disadvantages of Minimally Invasive Thyroid Surgery

One of the main limitations of minimally invasive thyroid surgery is that it is only suitable for a small number of patients with specific indications that meet the selection criteria. The procedure is also more technically demanding and has a longer operative time than traditional open thyroidectomy. Another disadvantage is that there is a learning curve associated with the procedure. It is also difficult for surgeons to gain experience with the technique. This is because the procedure is only suitable for a small number of patients, and the open technique is therefore more routinely performed.

If you have questions about thyroid nodules or thyroid surgery contact your local doctor, who will arrange for you to visit a thyroid surgeon.

References

[1] Timon C, Rafferty M. Minimally invasive video-assisted thyroidectomy (MIVAT): technique, advantages and disadvantages. Operative Techniques in Otolaryngology (2008) 19, 8-14.

[2] Rafferty M, Timon C. Minimal incision thyroidectomy. Operative Techniques in Otolaryngology (2008) 19, 2-7.

[3] Shimizu K. Minimally invasive thyroid surgery. Best Practice & Research Clinical Endocrinology and Metabolism (2001); 15(2):123-137.

[4] Rafferty M, Miller I, Timon C. Minimal incision for open thyroidectomy. Otolaryngology Head and Neck Surgery (2006); 135(2): 295-298.

[5] Miccoli P, Berti P, Raffaelli M, Conte M, Materazzi G, Galleri D. Minimally invasive video-assisted thyroidectomy. The American Journal of Surgery (2001); 181:567-570.

The post Minimally Invasive Thyroid Surgery appeared first on Thyroid Clinic Sydney.

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Thyroid dysfunction has thought to possibly contribute to memory disorders, such as Alzheimer’s disease and other types of dementia. Consequently, in patients who are experiencing memory problems, thyroid function tests are commonly ordered. A recent study aimed to see if elderly patients with hypothyroidism were more likely to suffer from mild cognitive impairment than elderly euthyroid individuals (those with normal thyroid function). Mild cognitive impairment is described as a state between normal age-related memory loss and dementia. It usually has minimal, if any, functional impact for the patient. Other studies on the topic have yielded conflicting results.

This study assessed cognitive function by face to face interviews and with detailed neurological and psychological tests. These tests looked at how well people performed in different areas of cognition, including memory, language, visuospatial, attention and executive function. In terms of thyroid function, patients were classified as either euthyroid, clinically hypothyroid or as having subclinical hypothyroidism. Clinical hypothyroidism was determined from medical records. Patients were deemed to have subclinical hypothyroidism if they had a thyroid stimulating hormone level of less than 10mIU/L, a free T4 level of 1.01 to 1.79ng/dL and were not on thyroxine therapy.

From the results of the cognitive testing, 316 of the 1904 participants in the study were found to have mild cognitive impairment, and the remaining 1588 patients were deemed to have normal cognitive function. Mild cognitive impairment was found in 16.3% of euthyroid participants, 17.2% of clinically hypothyroid patients and 17.7% of those with subclinical hypothyroidism. However, after the authors of this study accounted for other factors which were likely to influence the results (age, education, other medical conditions etc.), there was no significant influence of clinical or subclinical hypothyroidism on mild cognitive impairment.

A limitation of this study is that in the patients found to have mild cognitive impairment, there is no indication as to whether the hypothyroidism started before the onset of cognitive impairment or vice-versa. Additionally, the way the study was designed means that a cause-and-effect relationship cannot be determined.

Given the mixed results in other studies, more research is needed to determine the influence of hypothyroidism on cognitive function.

Reference

www.archneur.jamanetwork.com

Hypothyroidism and risk of mild cognitive impairment in elderly persons: A population-based study. JAMA Neurology; 71(2):201-207. Parsaik AK, et al. (2014).

The post Is there a link between Hypothyroidism and Mild Cognitive Impairment in the Elderly appeared first on Thyroid Clinic Sydney.

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By Ashleigh Elkins

There are many different tests that can be used to help confirm the diagnosis of a thyroid problem. Based on taking a history and performing a physical examination, if your doctor suspects you have a problem with your thyroid gland, he or she will most likely order one or more tests to help confirm or rule out the diagnosis of a thyroid disorder.

Common tests include blood tests to check the thyroid function, fine needle aspiration biopsy to evaluate lumps and nodules, and scans to obtain imaging of the thyroid gland.

Thyroid Function Tests

Thyroid function tests are a very common investigation performed when a thyroid problem is suspected. Thyroid function tests require a blood test. They are also used to monitor the effectiveness of treatment. Thyroid function tests assess the levels of thyroid stimulating hormone (TSH) and the two thyroid hormones – thyroxine (T4) and v (T3). These tests can be used to determine if the thyroid has a normal level of activity (euthyroid), if the thyroid is underactive (hypothyroid) or if the thyroid is over-active (hyperthyroid). The table below shows the results for the different states of thyroid activity:

Thyroid State TSH Free T4 Free T3
Euthyroid Normal Normal Normal
Hyperthyroid Decreased Increased Increased
Hypothyroid Increased Decreased Decreased

Due to Medicare restrictions in Australia, TSH needs to be tested alone first. If the TSH is found to be abnormal, then levels of thyroid hormone can be tested. This restriction does not apply to people who have already been diagnosed with a thyroid problem.

Thyroid Autoantibodies

Thyroid autoantibodies are another type of blood test that can be ordered in the investigation of thyroid problems. This test is used to rule in or rule out an autoimmune disease as the cause of thyroid problems. There are three main autoantibodies that can be tested for:

  1. Thyroid peroxidase antibodies (TPO); these are antibodies towards thyroid peroxidase, an enzyme that is needed in the process of producing T3 and T4. TPO antibodies are positive in most patients with Hashimoto’s thyroiditis and in most patients with Graves’ disease. TPO antibodies may also be elevated in patients with other autoimmune diseases, such as rheumatoid arthritis.
  2. Thyroglobulin antibodies; these antibodies are markers of autoimmune thyroid diseases. They are positive in almost all patients with Hashimoto’s thyroiditis and are positive in most people with Graves’ disease
  3. TSH receptor autoantibodies; these are antibodies that bind to the TSH receptor and cause it to activate. TSH receptor autoantibodies are positive in the majority of people with Graves’ disease.

Other Thyroid Blood Tests

There are a few other blood tests that may be ordered to investigate suspected thyroid disease. Calcitonin is a hormone made by the C cells of the thyroid and is released when levels of blood calcium are high. Calcitonin levels may be ordered in the investigation of people with thyroid nodules or suspected medullary thyroid cancer. Blood levels of calcitonin may be elevated in medullary thyroid cancer, and may be used in monitoring following treatment for medullary thyroid cancer. In addition, another blood test called carcinoembryonic antigen, or CEA, is also used in addition to calcitonin for monitoring and follow up after treatment of medullary thyroid cancer. CEA is also used for monitoring following treatment of other types of tumours, such as colorectal cancers.

Fine Needle Aspiration Biopsy

Fine needle aspiration biopsy is most commonly used in the investigation of thyroid nodules. The procedure involves inserting a needle into the nodule in order to remove a sample of cells which can then be analysed under a microscope to assist in diagnosis. There are usually several samples taken from different parts of the nodule to ensure that the samples that are taken are representative of the cells and tissues within the nodule. This test helps to determine whether or not the nodule requires surgical removal or further monitoring.

Fine needle aspiration can also be used to help evaluate thyroid cysts. This involves inserting a needle into the cyst and draining the fluid within the cyst. The fluid that is collected can be evaluated in the lab to see if there are any suspicious changes.

Fine needle aspiration biopsy is used to guide the treatment and management of patients with thyroid nodules. Thyroid fine needle aspiration cytology results are classified according to the Bethesda classification system which is a six-category system used to guide management of thyroid nodules.

The six categories of this system are:

  1. Unsatisfactory sample/Non-diagnostic
  2. Benign
  3. Atypia of undetermined significance
  4. Follicular neoplasm/suspicious for follicular neoplasm
  5. Suspicious for malignancy
  6. Malignant

Fine needle aspiration cytology cannot help to differentiate between benign and malignant follicular neoplasms. Ultrasound guidance can be used to visualise the nodule when performing the fine needle biopsy to make sure that the samples are being taken from within the nodule and not the surrounding thyroid tissue.

Nodules that are removed surgically undergo histopathological analysis to provide a definitive diagnosis.

Thyroid Imaging

Thyroid Ultrasound

Ultrasound is a safe, accurate, non-invasive, inexpensive and readily available imaging modality that can be used to assess the thyroid gland. Ultrasound is usually the first type of imaging ordered for the investigation of thyroid problems. Ultrasound uses sound waves transmitted through a hand-held transducer probe. A gel is placed over the neck which helps to transmit the ultrasound waves from the probe. There is no radiation used in an ultrasound. Thyroid ultrasounds are particularly useful for imaging thyroid cysts, nodules, goitre (enlargement of the thyroid gland) and suspected tumours. Ultrasounds can also be used to assess the blood flow in the thyroid. Ultrasound can also be used to guide fine needle aspiration biopsy of nodules or growths in the thyroid.

There are several ultrasound features which suggest that a thyroid nodule is likely to be benign. These include:

  • Sharp, well-defined borders around the entire nodule
  • Fluid within the nodule is indicative of the nodule being a cyst
  • Numerous nodules throughout the thyroid; this generally indicates a benign multinodular goitre
  • Minimal or no blood flow through the nodule indicates that the nodule is likely to be a cyst

Thyroid Scan/Thyroid Isotope Scans

An isotope scan of the thyroid is used to determine thyroid function because the scan measures how much of a substance similar to iodine is taken up by the gland. The thyroid uses iodine to produce thyroid hormones, so the thyroid normally absorbs iodine. For the scan, technetium (Tc- 99m) pertechnetate is injected. This is a substance that behaves similarly to iodine. Radioactive iodine has been used in the past, but technetium pertechnetate is now preferred because there is less radiation exposure and it is more cost-effective than radioactive iodine. After about 20 minutes, a scan is performed to identify the pattern of uptake in the thyroid.

This type of thyroid scan is particularly useful in helping to determine if the thyroid is over-active, such as in conditions like Graves’ disease, subacute thyroiditis and toxic multinodular goitre. All three conditions have different patterns of uptake:

Graves’ disease

  • Diffuse increased uptake

Subacute Thyroiditis

  • Low iodine uptake

Toxic Multinodular Goitre

  • Patchy uptake; areas of increased uptake and areas of decreased uptake

Thyroid isotope scans are helpful in the investigation of thyroid nodules. Thyroid nodules are generally classified as cold, warm or hot. A cold nodule does not take up any pertechnetate and is non-functioning, a warm nodule is functioning normally, and a hot nodule takes up more pertechnetate than the surrounding thyroid tissue and is said to be hyper-functioning. Isotope scans are particularly helpful for investigating patients with low levels of TSH. If a patient has low TSH and the isotope scan identifies a hot nodule, it is likely that the nodule is benign. Overall, the majority of thyroid nodules scanned are cold nodules, approximately 80%. However, only about 20% of cold nodules are found to be malignant after further investigation.

Thyroid CT Scan

Computed tomography, or CT scans can also be used to investigate suspected thyroid pathologies. It is not as good as ultrasound for identifying pathology within the thyroid gland itself, but CT is useful for investigating lymph nodes in the neck, chest and thyroid region. It is also used in the investigation of goitre to determine if the goitre has extended behind the sternum and into the mediastinum (retrosternal extension). CT may also be used if thyroid cancer is suspected to see if the tumour has spread to other surrounding organs. CT scans use x-rays to create cross-sectional images of the thyroid and surrounding structures. In some cases, a contrast medium may be injected to help define anatomical structures more clearly. A limitation of CT scans is that there is radiation exposure associated with the scan, unlike MRI and ultrasound.

Thyroid MRI Scan

Another type of investigation which may be ordered to investigate problems with the thyroid is a magnetic resonance imaging (or MRI) scan. Just like a CT scan, MRI is also not as good as ultrasound for detecting pathology within the thyroid gland itself. MRI scans might be ordered to assess surrounding lymph nodes and other neck and chest structures. It is useful to help determine if a suspected thyroid cancer has spread to surrounding organs. MRI can also be used to evaluate retrosternal goitre extension. MRI is also helpful to determine the size and shape of the thyroid. MRI may be recommended instead of a CT scan because there is no radiation exposure associated with an MRI, and an MRI scan of the thyroid does not usually require the administration of a contrast medium. CT and MRI are similar in terms of evaluating lymph nodes and spread to the surrounding tissues.

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Historically, fluoride was used as a treatment for hyperthyroidism; however, it is not a treatment that is currently used. Fluoride is thought to be an antagonist of iodine, impacting upon the ability of body tissues, such as the thyroid gland, to utilise iodine. However, this is only important if iodine levels are low. Fluoride is commonly added to drinking water supplies as a public health intervention in industrialised countries. This is because fluoride is an important component of the defence against tooth decay, and carries significant benefits for oral health. But is there an association between fluoridated water supplies and increased rates of hypothyroidism?

Recently, an English observational study was published. This study compared the levels of fluoride in the water in different regions of London with the prevalence of diagnosed cases of hypothyroidism at GP practices in the same region.

The authors of the study claimed that there was an increase in the prevalence of hypothyroidism in areas with higher levels of fluoride in the water¹.

However, this study has been criticised in the media by experts for flaws in the study’s methodology². Firstly, the study employs a very simplistic design to investigate whether or not there is an association. The authors do not take into account the numerous other potential confounding factors, which may influence the results of the study. This type of study design makes it virtually impossible to prove a cause-and-effect relationship between fluoridated water supplies and hypothyroidism because there are so many other factors that can influence the rates of hypothyroidism, for example iodine intake, beyond just the levels of fluoride in the water.

Furthermore, the levels of fluoride in the water are at a very low level in the water supply. These levels are significantly below the amount of fluoride needed to have an inhibitory effect on the thyroid gland. Experts quoted in the article in The Conversation² are critical of how the authors of the paper exaggerate the potential effect of fluoride on the thyroid gland, and do not give sufficient recognition to the potential influence of iodine deficiency on the results.

Due to the flaws in the methodology of this study, the results of this study should be interpreted with a degree of scepticism. Further studies with a better design are required to determine if there is a cause and effect relationship between fluoride in the water and hypothyroidism.

References

  1. Peckham S, Lowery D, Spencer S. Are fluoride levels in drinking water associated with hypothyroidism prevalence in England? A large observational study of GP practice data and fluoride levels in drinking water. J Epidemiol Community Health, 2015. Published online 24 February 2015. http://jech.bmj.com
  2. Rattan R. Flawed study overstates link between fluoride and ill health: experts. The Conversation. http://theconversation.com

The post Is there an association between fluoridated water and increased rates of hypothyroidism appeared first on Thyroid Clinic Sydney.

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