The essence in brief:
The thyroid gland is a small butterfly-shaped organ located below the Adam’s apple in the neck. It consists of two lobes connected by an isthmus.
Its primary function is to produce and release thyroid hormones, including thyroxine (T4) and triiodothyronine (T3), which play crucial roles in regulating metabolism and various bodily functions.
Thyroid hormones influence brain development, metabolism, fat breakdown, bone growth, muscle strength, nerve responsiveness, and heart function.
Imbalances in thyroid hormone production can lead to health issues. Hyperthyroidism is characterized by excess hormone production, while hypothyroidism results from insufficient hormone production.
The thyroid gland’s activity is controlled by the hypothalamus and the pituitary gland in the brain through a feedback mechanism.
Laboratories establish their own reference ranges for thyroid hormone levels, so the normal range may vary slightly from one lab to another.
In addition to its hormone-producing cells, the thyroid gland also contains C-cells, which produce calcitonin, a hormone involved in calcium regulation.
Overall, the thyroid gland is essential for maintaining various bodily functions, and disruptions in its hormone production can lead to a range of health problems.
The thyroid gland is a butterfly-shaped organ of approximately 20 milliliters in size. It wraps around the trachea below the larynx with a right and left portion (thyroid lobes). The connection between the lobes is called the isthmus. In women, a size of up to 17 ml is considered normal, while in men, up to 22 ml is considered normal.
The thyroid gland most important function is the production and release of thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones are found in the blood bound to transport proteins, but the active form is the free hormone fT3. In peripheral tissues, fT4 is converted to fT3 by removing one iodine molecule. Thyroid hormones are vital because they influence many processes in the body.
Effects of Thyroid Hormones:
Both a deficiency or excess production of these hormones can lead to disruptions in these processes, resulting in various symptoms and signs of thyroid disorders (see “Symptoms of Thyroid Disorders” for more information).
The production of thyroid hormones is tightly regulated by a feedback system. Malfunctions, whether overproduction (hyperthyroidism) or underproduction (hypothyroidism) of hormones, can lead to health problems.
The thyroid gland is controlled by the hypothalamus and the pituitary gland (hypophysis) in the brain. Disorders of the hypothalamus and the pituitary gland are rare, with thyroid gland malfunctions being the most common cause. The following simplified explanation illustrates the regulation of thyroid hormone production:
Image used under license from Shutterstock.com.
The described feedback loop maintains the levels of thyroid hormones necessary for normal development and a symptom-free life. When hormone levels are increased, for example, through the use of thyroid hormone tablets, the pituitary gland is inhibited. It releases less thyroid-stimulating hormone (TSH), reducing stimulation of the thyroid gland to produce hormones. Conversely, when little or no hormone is produced, as in the case of thyroid surgery, the inhibition of the pituitary gland is removed, leading to increased TSH release.
If TSH is lower than the lower limit of the normal range and fT3 and fT4 are elevated, the patient has hyperthyroidism (excess thyroid hormones). If TSH levels are above the age-appropriate normal range and fT3 and fT4 levels are low, the patient has hypothyroidism (insufficient thyroid hormones). If TSH is elevated above the age-appropriate normal range with normal fT3 and fT4 levels, it indicates subclinical hypothyroidism. If TSH is below the normal range with normal fT3 and fT4 levels, it indicates subclinical hyperthyroidism. If TSH is elevated along with elevated fT3 and fT4 levels, it may be due to receptor resistance (very rare) or a pituitary adenoma (only a few cases reported worldwide).
Each laboratory establishes its own reference range by testing samples from a few hundred healthy individuals. In a normal distribution, the top and bottom 5% are cut off, and the remaining 90% make up the reference range. 5% of people with a low TSH are still healthy, as are 5% with a high TSH. The thyroid gland also contains C-cells, which produce the hormone calcitonin (see the section on medullary thyroid carcinoma).
(This chapter provides information about the process of individual examinations. Not all examination steps are always necessary; in particular, scintigraphy and fine needle aspiration, as well as other examinations, are only carried out by specialized doctors for specific questions.)
Examination by the Doctor / “Anamnesis”
The essence in brief:
The examination process for thyroid diseases begins with a doctor’s anamnesis, which involves precise questioning about symptoms, their severity, and medication history. Typical symptoms of hyperthyroidism include nervousness, sweating, and rapid heart rate, while hypothyroidism symptoms include fatigue and weight gain. The text also mentions neck and eye complaints associated with thyroid issues. It emphasizes the importance of prompt examination for certain symptoms, like rapid goiter growth or hoarseness.
Like any examination with a doctor, thyroid examination also begins with precise but targeted questions from the doctor (anamnesis). First, symptoms are assessed, then questions about thyroid problems are asked. The chronological sequence and severity of the symptoms are very important, especially in relation to the medications taken and their dosages. You can prepare for your doctor’s appointment by bringing a dosing plan of the current medications and supplements you have taken in recent weeks and months. A detailed dosing plan includes the name, strength (e.g., milligrams of the medication), and the number of tablets taken per day.
The symptoms of thyroid diseases are often typical and can be well attributed by an experienced doctor. However, the severity of the symptoms varies widely depending on the duration and intensity of dysfunction, age, and the individual’s sensitivity.
Below are typical symptoms and signs of illness:
SYMPTOMS OF OVERACTIVITY / HYPERTHYROIDISM
The symptoms of overactivity are similar to an inner tension, as if one were preoccupied before a major event or an exam.
Nervousness and restlessness, sleep disturbances, and difficulty concentrating, irritability
Sweating and hair loss
Tremors, muscle weakness
Diarrhea
Weight loss with increased appetite
Rapid heartbeat, heart palpitations (arrhythmias), high blood pressure
Irregular or absent menstrual periods, infertility
SYMPTOMS OF UNDERACTIVITY / HYPOTHYROIDISM
Overall bodily activity is reduced.
Fatigue and lack of drive, weakness, depression, difficulty concentrating
Feeling cold, dry skin, swelling of the skin, dull hair, and hair loss
Constipation
Weight gain with reduced appetite
Slow pulse, low blood pressure
Irregular or absent menstrual periods, infertility
Sometimes the combination of symptoms is so typical that the diagnosis is not difficult. However, many patients have similar symptoms even when thyroid disease is not present. Some symptoms are also found in both overactivity and underactivity. All of these symptoms can also occur with other illnesses. Older people often complain of weakness, depressive mood, and constipation even without thyroid dysfunction.
COMPLAINTS IN THE NECK
Depending on the size of the thyroid gland and the location of nodules, pressure in the neck can occur, sometimes only when swallowing. However, difficulty swallowing or even shortness of breath only occur with very large enlargements or very large nodules.
Distinguishing from this are pains when swallowing or under pressure, which can occur in specific rare forms of thyroid inflammation and when nodules or cysts bleed into them. The pain is described as sharp, and often, the pain radiates from the neck to the ear.
COMPLAINTS IN THE EYES
Specific thyroid diseases can cause eye problems.
Eye complaints with thyroid diseases:
Rubbing (feeling like sand in the eyes) and tearing of the eyes
Light sensitivity
Swelling of the eyelids
Enlarged eyelid opening (making the eye appear larger)
Pressure behind the eye, increasing when looking upward
In later stages, conjunctivitis and double vision
COMPLAINTS THAT SHOULD BE URGENTLY CLARIFIED
In some cases, it is not certain whether symptoms are caused by the thyroid or have other causes. However, they should be promptly clarified through a thyroid examination because they may require urgent treatment:
Complaints that should be urgently clarified:
Rapidly growing goiter
Sudden hoarseness
Cough
Swallowing difficulties and shortness of breath
Enlargement of lymph nodes
The meaningfulness of ultrasound examination regarding malignancy
Whether a nodule is suspicious of being malignant is predominantly assessed today using ultrasound examination alone.
For the evaluation of the nodules, there are recommendations that were updated in 2017:
ACR TI-RADS 2017 see chapter nodules).
Fine-needle aspiration
The essentials in brief
Fine-needle aspiration: A medical procedure for obtaining cells from the thyroid gland, nodules, cysts, or lymph nodes.
Fine-needle aspiration allows for the direct removal of cells from the thyroid gland, nodules, cysts, or lymph nodes, which can then be evaluated under a microscope after specific staining (cytology). Fine-needle aspiration is the most reliable method, without surgery, to establish a clear diagnosis. It is used to investigate tissue regions that are unclear on ultrasound, such as nodules, and is performed under ultrasound guidance using a very fine needle.
The aspiration is harmless and in terms of pain, it is comparable to a simple blood draw. Anesthesia is not necessary. It takes only a few seconds and is performed on an outpatient basis. After the aspiration, your ability to drive and work is not affected. The often-feared “spreading” of potentially existing tumor cells does not occur.
Scintigraphy
The key points summarized briefly:
The strength of scintigraphy is to reflect the function of the thyroid gland as a whole and its individual parts. However, due to its two-dimensional imaging technique, it is less suitable than ultrasound examination for representing the spatial dimensions of the thyroid gland and its components.
The basis of scintigraphy technique lies in the thyroid gland’s property to take up iodine to produce hormones: Active thyroid glands/thyroid parts will require and want to take up more iodine than less active or inactive parts. The “greed” for iodine uptake is directly proportional to the activity of the thyroid gland parts.
In scintigraphy, a substance (Technetium) is offered to the thyroid gland, which behaves similar to iodine and emits radioactive rays that can be measured. Examples:
A highly active, e.g., overactive thyroid gland will bind a lot of iodine substitute, resulting in very high measurable radioactivity over the thyroid gland.
A non-hormone-producing nodule will not bind iodine substitute, and there will be no measurable radioactivity over this nodule (known as a “cold nodule”).
For scintigraphy outside of a hospital stay, Technetium99m is typically used. This substance has several advantages over radioactively labeled iodine, including lower radiation exposure, a shorter half-life, favorable physical properties for scintigraphy, and greater availability. However, in specific cases, an iodine scintigram (Iodine123) must be performed (advantages over Tc99m: better visualization of the thyroid gland/parts, uptake and metabolism by the thyroid gland).
Scintigraphy is a radiological examination. The radiation exposure is comparable to a chest X-ray. The procedure is subject to strict conditions:
Examination by specialized physicians only
No examination for pregnant or breastfeeding mothers
Examination in children only in urgent cases
Explanation of the advantages and disadvantages, exclusion of pregnancy if necessary
If necessary, emptying the bladder before the examination (Tc is excreted through urine)
Examination in a specially shielded area of the practice to protect against radiation
Injection of Tc99m through the vein (similar to a blood draw; no allergies, no side effects or discomfort, the administration is not felt)
The substance must now distribute in the body, find its way from the arm to the thyroid gland. The waiting time varies depending on the examination technique, usually ranging from 5 to 20 minutes. During this time, your body emits radioactive radiation. Therefore, you must not leave the specially protected area of the practice (e.g., not go to the waiting area or the restroom!)
After this period, you will be placed in front of a camera for 5 minutes (occasionally examined while lying down) to measure the radiation. To ensure a clear spatial allocation of the individual parts, you should move as little as possible.
After the examination, the radiation has decreased enough to allow you to leave the specially shielded area of the practice and the practice itself.
To evaluate the scintigram, the doctor needs to know the ultrasound examination results and the thyroid function (TSH levels). The assessment involves both the overall uptake of Technetium and the distribution of radioactivity over the thyroid gland’s surface, such as in the area of nodules.
Thyroid nodules that are <1 cm in size cannot be visualized with scintigraphy. Cold nodules are overshadowed by the surrounding tissue. Scintigraphy should always be performed for nodules over 1 cm in size to reliably identify warm nodules. To determine the need for surgery in cases of suspected malignancy, an ultrasound examination possibly supplemented by fine-needle aspiration is sufficient. Even a scintigraphic cold nodule should only be operated on if the sonography criteria