Table of Contents
What is Hypothyroidism?
Hypothyroidism is the manifestation of an underactive thyroid due to a deficiency in the circulating levels of thyroid hormones. Hypothyroidism symptoms and signs occur in many systems of the body and could also occur in Newborn children in this case, it leads to a condition known as Cretinism characterized by neurologic impairment and mental retardation. Hypothyroidism may also be associated with deafness such as in Pendred’s syndrome and Turner’s syndrome.
There are different types of Hypothyroidism which are classified based on the cause of the Hypothyroidism into the following:
- Primary Hypothyroidism
- Secondary Hypothyroidism
- Tertiary Hypothyroidism
Primary Hypothyroidism occurs when the cause of an underactive thyroid arises from the thyroid gland. Problems such as autoimmune disorders (Hashimotos Thyroiditis, Radioactive Iodine Therapy for Graves Disease) or Thyroidectomy surgery are classified as Primary causes of Hypothyroidism.
Secondary Hypothyroidism occurs when the cause of hypothyroidism arises from the pituitary gland. Diseases such as pituitary cancer and pituitary ablation lead to Secondary Hypothyroidism.
Tertiary Hypothyroidism arises from diseases affecting the Hypothalamus. Medical conditions such as hypothalamic insufficiency give rise to tertiary hypothyroidism.
Causes of Hypothyroidism could be primary, secondary or tertiary depending on whether the hypothyroidism arises from the Thyroid gland, pituitary gland or the Hypothalamus respectively. The causes of Hypothyroidism include:
Primary causes of Hypothyroidism
- Autoimmune diseases such as Hashimotos thyroiditis, and Postpartum thyroiditis
- Radioactive Iodine Therapy for Graves disease
- Post thyroidectomy
- Excessive Iodine intake especially in drugs such as amiodarone, radiocontrast agents, expectorants containing potassium iodide and kelp
- Subacute thyroiditis
- Prolonged use of lithium containing drugs such as Lithium carbonate
- Use of antithyroid drugs such as methimazole or carbimazole
- Iodine deficiency in the diet
- Dyshormogenesis (abnormal formation of thyroid hormones)
Secondary Causes of Hypothyroidism
- Pituitary cancers
- Pituitary ablation
- Pituitary resection
Tertiary Causes of Hypothyroidism
- Hypothalamic insufficiency
- Resistance to thyroid hormone
This is a condition in which serum thyroxine (T4) and T3 levels are normal with moderate rise in serum TSH levels.
Grading of Subclinical Hypothyroidism
- Grade 1: there is a moderate rise of about 5-10
- Grade 2: a moderate rise of 10.1-20
- Grade 3: a rise of more than 20
All patients with subclinical hypothyroidism should be treated.
Hypothyroidism Symptoms in Women and Men
Symptoms of Hypothyroidism include:
- Failure of children to grow and develop properly leading to dwarfism and severe mental retardation (a condition called Cretinism)
- Muscle cramps (myalgia)
- Fatigue (feeling tired)
- Weight gain despite decrease in appetite
- Cold intolerance (easily feeling cold even when others are not cold)
- Change in voice (hoarse or husky voice)
- Cold intolerance
- Poor memory
- Change in appearance
- Poor libido (lack of sexual drive)
- Arthralgia (painful joints)
- Muscle weakness/Stiffness
- Oligomenorrhoea in women (longer cycle of menstrual cycle)
Hypothyroidism Signs in Women and Men
Signs of Hypothyroidism include:
- Features of hypopituitarism such as pale and waxy skin, loss of body hair and atrophic genitalia may be present when due to pituitary failure
- Cardiovascular changes such as Bradycardia, Hypertension, Cardiomegaly, decreased cardiac output, pulmonary effusions, pericardial effusion and anemia
- Myxedema characterized by facial swelling with swelling around the eyes (periorbital puffiness), rough and dry skin, dry and brittle hair (causing severe hair loss), slowed speech
- Myxedema madness – dementia
- Infertility in both males and females
- Macroglossia (large tongue)
- In children, there will be developmental delay, abdominal distention, development of umbilical hernia and rectal prolapse.
- Hypothyroidism in women causes Menorrhagia (Heavy menstrual flow)
Thyroid Test for Hypothyroidism (Underactive Thyroid Test)
Underactive thyroid test (which are the laboratory investigations or tests for Hypothyroidism) include thyroid blood test and scan.
- In Hypothyroidism, there is decreased serum levels of T 4 and T3 (Triiodothyronine) with associated increased in Thyroid Stimulating Hormone (TSH) in primary hypothyroidism. In Secondary Hypothyroidism, the T4, T3 and TSH are all decreased but in this, the TSH does not increase with Thyrotropin Releasing Hormone (TRH) stimulation Test. TRH which is produced from the Hypothalamus causes the release of TSH from the anterior pituitary gland.
- There is elevated Thyroid autoantibodies in Hashimoto’s thyroiditis Hypothyroidism
- There is hyponatremia and retention in comatose patients with myxedema
- ECG Findings show decreased voltage with flattening or inversion of T waves and P waves with prolongation of QT interval.
Treatment of Hypothyroidism is by use of oral thyroxine which is a replacement therapy.
Thyroxine is given in doses of 50 to 200g per day, depending on Patient’s size and condition. It is started on 25 to 50g daily in the elderly who are having coexisting heart disease or profound hypothyroidism because of associated hypercholesterolemia and atherosclerosis.
A baseline ECG is done in patients with severe hypothyroidism prior to treatment to help in monitoring the cardiac changes so as not to tilt the patient into Thyrotoxicosis due to excessive blood levels of thyroxine. The Thyroxine dosage should be adjusted to suit clinical response and till TSH levels return to normal. For Patients in myxedema coma, they require an initial emergency intravenous dose of thyroxine (300 to 400 g) and careful Intensive Care Unit (ICU) monitoring.
Complications of Hypothyroidism include:
- Weight gain predisposing to Cardiovascular diseases
- Cardiovascular complications of hypothyroidism such as Bradycardia, Elevated blood pressure, Pericarditis, Pericardial effusion, Coronary artery disease, diminished Cardiac output and Cardiac failure
- High low-density lipoprotein, low high-density lipoprotein levels, and hypercholesterolemia
- Neurological complications of hypothyroidism such as delayed deep tendon reflexes (Woltman’s sign), Carpal tunnel syndrome, Peripheral neuropathy, Myxedema madness, Myxedema coma and Pseudodementia. Others include Deafness to high tones (Trotter’s syndrome)
- Mental retardation
- Hypothyroidism in pregnancy may increase the risk of premature delivery and newborn babies with low birth weight.