What Is Thyrotoxicosis?

Thyrotoxicosis is a medical condition characterised by excessive thyroid hormones circulating in the body. Hyperthyroidism is often confused with thyrotoxicosis. Let's clear up the confusion between the two. Hyperthyroidism is due to an overactive thyroid gland, which results in the production and release of excessive thyroid hormones. By comparison, thyrotoxicosis is the clinical state of having excess thyroid hormones in the body due to any reason, such as taking more than the recommended dose of thyroid medication or due to hyperthyroidism. So, hyperthyroidism is a form of thyrotoxicosis. Thyrotoxicosis is rare, affecting around 2% of people assigned female at birth (AFAB) and 0.2% of people assigned male at birth (AMAB).¹ 

Thyroid gland

Let's discuss the thyroid gland and the hormones it releases to help us better understand thyrotoxicosis. The endocrine glands make and release hormones, which act as chemical messengers in the bloodstream to coordinate different functions in the body. The thyroid is a small, butterfly-shaped endocrine gland situated in the front of your neck. It helps in controlling the body’s metabolism (the process by which your body converts food into energy). 

The thyroid gland makes and releases these hormones:

• Thyroxine (T4): It is the primary hormone made and released by the thyroid gland. It contains four atoms of iodine. T4 is the inactive form of thyroid hormone, meaning that it does not impact cells in the body. Once the thyroid gland releases T4, certain organs in the body transform it into T3 (the active form of thyroid hormone). 
• Triiodothyronine (T3): It is secreted (released) in a lower quantity than thyroxine. It is made up of three atoms of iodine. T3 is the active form of thyroid hormone, meaning that it impacts the body’s cells and metabolism. T3 works with T4, and collectively, they are referred to as “thyroid hormone”.
• Calcitonin: It helps in regulating the amount of calcium in the blood. Calcitonin does not impact the body’s metabolism like T4 and T3 do.

Iodine is important for the thyroid gland in helping to make thyroid hormones. An excess or deficiency of iodine in the body can cause thyroid disorders, leading to altered body functions. Good sources of iodine are seafood and dairy products.

Let's discuss a few thyroid disorders:

• Hypothyroidism: Hypothyroidism happens due to an underactive thyroid gland, which results in a deficiency of thyroid hormones in the body, causing the metabolic rate to slow down. Symptoms include tiredness, weight gain, and depression. 
• Hyperthyroidism: Hyperthyroidism is caused by an overactive thyroid gland, which results in excessive thyroid hormones in the body. It speeds up the body's metabolism. Symptoms include weight loss, trembling, sensitivity to heat, mood swings, and rapid heart rate.
• Goitre: Goitre is characterised by a lump or swelling of the thyroid gland, which can cause difficulty in breathing or swallowing. 
• Thyroiditis: Thyroiditis refers to inflammation of the thyroid gland. It can lead to an excess or deficiency of thyroid hormones. 
• Graves' disease: Graves' disease is an autoimmune disorder that can result in hyperthyroidism. Symptoms include anxiety, weight loss, or irregular heartbeat.
• Hashimoto's disease: Hashimoto's disease is an autoimmune disorder where the body's immune system starts attacking the healthy tissues, resulting in hypothyroidism. Symptoms include increased sensitivity to cold, fatigue, or muscle weakness.
• Thyroid cancer: Thyroid cancer is a cancer of the thyroid gland. The four main types of thyroid cancer are papillary, follicular, medullary, and anaplastic. 

Causes of thyrotoxicosis

Thyrotoxicosis is caused due to the following reasons.¹

• Hyperthyroidism – when the body makes and releases too many thyroid hormones. This is the most common cause of thyrotoxicosis.
• Graves' disease – the most common cause of hyperthyroidism. 
• Toxic adenoma – a benign (non-cancerous) single thyroid nodule (growth) causing an excess of thyroid hormones.
• Toxic multinodular goitre – several benign (non-cancerous) nodules (growths) in the thyroid gland that produce too much thyroid hormone.
• Postpartum thyroiditis – inflammation of the thyroid gland that can happen after a woman has a baby. It is often a temporary condition.
• Subacute thyroiditis – a temporary inflammation of the thyroid caused by a virus.
• Consuming excess thyroid medication.

Symptoms of thyrotoxicosis

Thyrotoxicosis is characterised by the following symptoms:¹^,²^,³

Appearance

• Enlarged thyroid gland

Cardiovascular symptoms 

• Tachycardia (an abnormally rapid heart rate of over 100 beats per minute)
• Shortness of breath
• Palpitations (the sensation that your heart is pounding or racing)
• Atrial fibrillation (an irregular heart rhythm)
• Heart failure

Gastrointestinal symptoms 

• Weight loss
• Increased appetite
• Diarrhoea

Neuromuscular symptoms 

• Insomnia
• Mood swings
• Psychosis
• Tremor
• Anxiety
• Muscle weakness

Reproductive system symptoms 

• Irregular periods among people AFAB
• Reduced sex drive
• Reduced fertility 

Skin symptoms

• Hair loss
• Increased sweating
• Heat intolerance

Diagnosis of thyrotoxicosis

If you suspect you are suffering from thyrotoxicosis, contact your GP. Healthcare professionals will use physical tests and some diagnostic procedures to rule out thyrotoxicosis.¹^,²^,³^,⁴

• Physical examination: Your healthcare provider will examine your neck to check for swelling or enlargement. They might also check for swelling or redness in the eyes, tremors in the hands or check for rapid heart rate. 
• Blood tests: Your healthcare provider will take a blood sample to check the level of thyroid hormones. These tests are called Thyroid Function Tests (TFT). Increased levels of T3 and T4 along with reduced levels of TSH indicate thyrotoxicosis. Two sets of TFT done at an interval of six weeks can confirm the diagnosis. Low levels of TSH with normal T3 and T4 levels are subclinical thyrotoxicosis. 
• Ultrasound: Ultrasound is a non-invasive radiological procedure that provides images of the thyroid gland. It can be used to check for nodules in the neck.
• Thyroid scan: This involves the injection of radioactive tracer into a vein in the arm or hand, followed by imaging after 15-20 minutes. The radioactive tracer gives off gamma rays, which are similar to X-rays. An imaging camera is focused on the neck region, and the thyroid gland is visualised as it detects the gamma rays. This scan helps in distinguishing different types of thyroid disorders.
• Radioactive iodine uptake (RAIU) test: This is another radiological procedure involving radioactive iodine in the form of liquid or pill. After 6 hours and 24 hours, the neck is scanned to check the radiotracer uptake by the thyroid gland. 

Treatment of thyrotoxicosis

If thyrotoxicosis is confirmed, then your physician will start a treatment plan according to the severity and cause of the condition.¹^,²^,³

• Antithyroid drugs: These drugs are also called thionamides. Medications such as carbimazole and propylthiouracil (PTU) help in reducing thyroid hormone production. It can also help in reducing the conversion of T4 to T3. Side effects can include fever, rash, urticaria (hives), and hepatotoxicity (damage to the liver caused by a medicine). 
• Radioactive iodine therapy: Radioactive iodine (RAI) can be administered as an oral capsule to treat Graves' disease or toxic multi-nodular goitre. It is a safe and generally well-tolerated treatment that specifically targets thyroid cells and damages or destroys them through radiation. Women who are pregnant or breastfeeding should not receive RAI therapy as radiation might harm the foetus and reach the baby through breast milk. In the majority of cases, patients develop hypothyroidism after this therapy and require thyroid medications throughout their life. 
• Surgery: Surgery can be performed to remove either a part of the thyroid or complete removal of the thyroid gland (thyroidectomy), depending on the condition of the patient. The majority of patients develop hypothyroidism (underactive thyroid). They will require thyroid medications throughout their life to top up the level of thyroid hormone produced by the remaining thyroid gland. Potential complications of thyroid surgery include laryngeal nerve injury or permanent hypoparathyroidism. 
• Beta-blockers: Beta-blockers help in blocking the action of thyroid hormones in the body. They are effective in managing the symptoms of thyrotoxicosis (e.g. heart rate, anxiety or sweating), not in the reduction of thyroid hormone levels. They can be useful in older patients or patients with cardiovascular diseases. 

Prevention of thyrotoxicosis

Thyrotoxicosis can be caused by a variety of factors. There are no set guidelines on how to prevent thyrotoxicosis. Sometimes, consuming more than the recommended doses of thyroid medication can cause thyrotoxicosis so it is essential to take thyroid medication as prescribed by your doctor. 

A family history of thyroid disease increases your chance of being diagnosed with thyrotoxicosis. So, if you feel any symptoms, contact your GP immediately.  

Postpartum thyroiditis (inflammation of the thyroid) sometimes occurs in women after childbirth. This can also cause thyrotoxicosis. So, if you just had a child and are feeling unwell, contact your healthcare provider.

Summary

Thyrotoxicosis is a treatable medical condition characterised by excessive thyroid hormones in the body. It affects around 2% of people AFAB and 0.2% of people AMAB. The thyroid gland produces two main hormones; T3 and T4. They help in maintaining the metabolic rate of the body (i/e/ the rate at which the body converts food into energy). An increase in thyroid hormone alters the body's functions and causes some health problems. Symptoms of thyrotoxicosis include an enlarged thyroid gland, shortness of breath, weight loss, insomnia, anxiety, palpitations, irregular periods, reduced fertility, and hair loss.

Thyrotoxicosis can be caused by Graves' disease, postpartum thyroiditis, multi-nodular goitre, subacute thyroiditis, toxic adenoma, or hyperthyroidism.

Diagnosis of thyrotoxicosis may involve a physical examination,  blood tests, ultrasound, thyroid scanning, and radioactive iodine uptake tests. 

Treatment options include antithyroid medications, beta-blockers, radioactive iodine therapy, or surgery.