Hyper- and Hypo- thyroidism

The thyroid gland is a component of the endocrine system and is responsible for the synthesis and release of two principal hormones – triiodothyronine (T3) and thyroxine (T4), using iodine obtained from our diet.

Position of the thyroid gland
Illustration from MSD Manuals

The thyroid gland is regulated by the hypothalamus and pituitary glands in the brain, which are also components of the endocrine system.

Human endocrine system
Illustration from US Environmental Protection Agency
Regulation and synthesis of thyroid hormones
Illustration adapted from Vail Ranch Pharmacy

Thyroid hormones are involved in the regulation of several vital functions in the body including digestion and burning of calories, heart rate, thermoregulation, muscular contraction and replacement of dying cells.

Hyperthyroidism refers to the condition where the thyroid gland is overactive and produces thyroid hormones in excess. Hypothyroidism refers to the thyroid gland being underactive and producing insufficient thyroid hormones. Both conditions can result in different symptoms and consequences that have been discussed below.

Symptoms

Symptoms for hyperthyroidism and hypothyroidism may include the following:

HyperthyroidismHypothyroidism
. weight loss (sometimes despite an increased appetite)
. goitre (enlarged thyroid gland visible as a swelling on the neck)
. hyperactivity, anxiety, nervousness, irritability, mood swings
. fatigue or muscular weakness
. difficulty sleeping
. more frequent urination and/or diarrhoea
. persistent thirst
. hair thinning and/or patchy hair loss
. increased skin sensitivity
. itchy skin or urticaria
. increased heat sensitivity
. increased sweating
. twitching or tremors (particularly in hands/fingers)
. irregularities in menstrual cycle
. decreased libido  
. weight gain (sometimes including a puffy face)
. goitre
. fatigue or muscular weakness/cramps
. constipation
. voice hoarseness
. hair thinning and/or brittle hair/nails
. dry/flaky skin
. increased cold sensitivity
. pain, numbness or tingling (mostly in the hands/fingers)
. aching joints
. irregular or heavier menstruation
. decreased libido





Complications

Given that the thyroid gland and the hormones it synthesises are involved in the regulation of many body functions, there are further complications that could arise from an overactive or underactive thyroid. These include:

HyperthyroidismHypothyroidism
. atrial fibrillation (heart rhythm disorder) leading to tachycardia (increased heart rate), arrhythmia (irregular heartbeat) or, in extreme case, heart failure
. palpitations (heart pounding)
. osteoporosis
. Grave’s ophthalmopathy (causing increased light sensitivity, blurring, double vision, red/swollen eyes, eye bulging, watery or dry eyes)
. problems in pregnancy (such as miscarriage, premature birth, pre-eclampsia)
. thyroid storm / thyrotoxic crisis (occurs rarely and involves a sudden flare-up of symptoms, leading to an increased heart rate, fever, sometimes jaundice, delirium and possible unconsciousness)  
. reduced heart rate
. elevated blood cholesterol levels and subsequent arterial blockage
. problems in pregnancy (such as miscarriage, premature birth, pre-eclampsia)
. depression
. memory impairment
. hearing impairment
. anaemia
. myxoedema coma (occurs rarely but is life-threatening and may require treatment with antibiotics, steroids and even ventilation)  

Causes

In general, women appear to be at a higher risk of developing thyroid conditions, with those over the age of 60 years having a greater risk of hypothyroidism. Individuals with a family history of thyroid disease or other conditions that may give rise to thyroid disease (see below) are also at a higher risk, as are those with chronic conditions such as Type 1 diabetes and a few other long-term medical conditions.

There are several reasons that could account for the incidence of hyperthyroidism or hypothyroidism. These include:

HyperthyroidismHypothyroidism
. Grave’s disease, an autoimmune condition which attacks the thyroid gland and causes it to be overactive (most common in young to middle-aged women, particularly if there is a family history of the condition, and in smokers)
. benign thyroid nodules (conditions such as Plummer’s disease)
. pituitary adenoma (benign pituitary gland tumours)
. medication with high levels of iodine
. elevated levels of human chorionic gonadotrophin (hCG) hormone, usually in early pregnancy, multiple pregnancy or molar pregnancy
. thyroiditis
. thyroid cancer, in rare cases





. autoimmune conditions that attack the thyroid gland (commonly Hashimoto’s disease )
. over-reaction to or excessive treatment for hyperthyroidism
. damage to or other medical issues of the pituitary gland
. thyroid surgery (partial or complete removal of the thyroid gland), radiation therapy focused on the head/neck regions
. medication with high levels of lithium (used in psychiatry), amiodarone (used to treat arrhythmia) or interferons (used to treat hepatitis C and some cancers)
. lack of dietary iodine
. congenital disorder where some babies are born with defective or no thyroid gland  

Diagnosis

If symptoms such as those mentioned above are observed, your GP is most likely to first carry out a thyroid function test, which involves drawing a blood sample to test for levels of:

  • thyroid stimulating hormone (TSH)
  • triiodothyronine (T3), sometimes referred to as free triiodothyronine (FT3)
  • thyroxine (T4), sometimes referred to as free thyroxine (FT4)

Low TSH with high levels of T3 and/or T4 may imply hyperthyroidism.

High TSH with low T4 may imply hypothyroidism. If TSH is high but T4 is at a normal level, this could imply a risk of hypothyroidism in the future.

If abnormal levels of these hormones are detected in your blood, your doctor may subject you to further testing such as blood tests for anti-thyroid antibodies (to test for conditions such as Grave’s disease), and erythrocyte sedimentation rate (ESR) (to test for inflammation).

A thyroid scan may also be recommended to test for thyroid nodules.

Prevention

There is little that can be done to prevent the incidence of an overactive or underactive thyroid. A couple of simple things to bear in mind would be try to maintain a balanced diet that has a sufficient by not excessive level of iodine, and to be mindful of any new medications or treatments that are prescribed for other medical conditions and to discuss potential side effects with your doctor.

Treatment

Based on the patient’s condition, one or more of the following measures may be considered towards the treatment of hyperthyroidism:

  • thionamide medication (such as carbimazole, propylthiouracil) to reduce the synthesis of thyroid hormones
  • beta-blockers to help alleviate some of the associated symptoms
  • radioactive iodine treatment to destroy some cells around the thyroid gland, thereby reducing hormone production (prolonged close contact with pregnant women and children should be avoided for a few days or weeks depending on treatment dosage; recipients should also avoid getting pregnant/fathering children for a recommended number of months)
  • thyroidectomy, where all or part of the thyroid is removed surgically (it would be necessary to take medications for the rest of your life to maintain the required level of thyroid hormones in the body)

Medication for hyperthyroidism is known to bring about side effects in most patients. These should therefore be discussed and accounted for with your doctor prior to commencement of treatment. Dosages may be altered over time to adjust to your body’s response.

Treatment for hypothyroidism is quite standard and generally involves taking levothyroxine which replaces the missing thyroid hormones. Dosage would be determined by your doctor depending on your current condition, and may be altered over time. This medication would ideally need to be taken for life, ideally at the same time every day. Side effects of levothyroxine are generally mild, if at all, but it is important that dosage is controlled according to how your body is responding, so as to avoid any unpleasant reactions.

Cover illustration from Cleveland Clinic Health Essentials

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