Related Subjects:
|Thyrotoxicosis and Hyperthyroidism
|Thyroid Storm - Thyrotoxic crisis
|Graves' Disease (Thyrotoxicosis)
|Amiodarone and Thyroid disease
|Thyroid Surgery (Thyroidectomy)
|Hypothyroidism
|Hashimoto's thyroiditis
|DeQuervain's thyroiditis
|Subacute Thyroiditis
|Thyroid nodule
|Congenital Hypothyroidism
|Thyroid Function Tests and antibodies
|Post partum thyroiditis
|Sick Euthyroid Syndrome
|Thyroid Exam (OSCE)
|Thyroid Gland anatomy and Physiology
|Thyroid Cancer
Start with a lower dose of Thyroxine in the elderly and in those with angina or heart failure
Introduction
- Hypothyroidism is a disease in which there is inadequate production of thyroxine for normal physiological functions.
- The thyroid gland requires iodine to make thyroxine. The gland produces both T4 and T3 molecules but T3 is the most active form.
- Generally the T4 level is low but in clinical care, the best test for hypothyroidism is a raised TSH.
- This has been found to be an exquisitely sensitive indicator of thyroid status.
- A normal TSH result suggests adequate thyroid hormone replacement and euthyroidism.
Aetiology
- Primary hypothyroidism (95% of cases) occurs when the thyroid gland is unable to produce T3/T4 because of iodine deficiency or an abnormality within the gland itself
- Secondary "pituitary" hypothyroidism is the result of insufficient production of bioactive TSH release because of a pituitary or hypothalamic disorder
Causes of primary hypothyroidism
- There are a variety of these from surgical removal or radiotherapy of the gland to iodine deficiency and inflammatory conditions
- Iodine deficiency: iodine deficiency is the most common cause of hypothyroidism. Seen worldwide.
- Autoimmune thyroiditis such as Hashimoto's or atrophic thyroiditis where there is the destruction of thyroid follicular cells by lymphocytes. It may be associated with a goitre (Hashimoto's thyroiditis) or occur without a goitre (atrophic thyroiditis or primary myxoedema)
- Post-ablative therapy or surgery: after surgery, radioiodine therapy, or external radiotherapy
- Drugs: Anti-thyroid drugs for Graves' disease (such as carbimazole and propylthiouracil) will develop hypothyroidism 10-20 years later. Treatment with several other drugs, such as iodine (including kelp supplements), amiodarone, lithium, interferons, thalidomide, and rifampicin
- Transient thyroiditis: Subacute (de Quervain's) thyroiditis with painful swelling of the thyroid gland thought to be caused by a viral infection
- Postpartum thyroiditis (PPT) is the development of thyrotoxicosis, hypothyroidism, or thyrotoxicosis followed by hypothyroidism within a year of giving birth, in women who were euthyroid prior to pregnancy
- Thyroid infiltrative disorders: amyloidosis, sarcoidosis, haemochromatosis, tuberculosis, and scleroderma
- Congenital hypothyroidism: absence or underdevelopment of the thyroid gland (60%), an ectopic hypoplastic gland (30%), or the absence of enzymes required for thyroid hormone synthesis and iodide transfer
Clinical
- Rare but must know about Myxoedema coma (See topic)
- Clinically hypothyroid, Tiredness, lethargy, weight gain
- Depression, constipation, cold intolerance
- Poor memory, slowness, depression, dry and cold skin
- Heavy or infrequent periods, psychosis
- Ataxia and slowness of movement
- Dry thin hair, hypothermia, bradycardia
- heart failure, pericardial effusion, weight gain and obesity
- "hung up" slow relaxing reflexes and Myotonia and proximal myopathy
- Children develop cretinism if congenital hypothyroid
Before and after starting Thyroxine
Some may have a Goitre
Differential
Investigation
- FBC: anaemia, macrocytes
- CXR: pleural effusion, pericardial effusion
- ECG: bradycardia, low voltage
- TFTS: high TSH low T4 and T3 unless pituitary disease and T4 and TSH usually low/normal or even mildly elevated
- Thyroid ultrasound if enlarged or nodules
Classification
- TSH high usually >10 , T4 is below normal range: Treats as Primary hypothyroid
- TSH high, T4 is normal: Subclinical hypothyroid. Treat if TSH >10 or symptoms or peroxidase positive
- TSH high, T4 above normal range. Endocrine referral
- TSH normal: Normal Euthyroid patient
- TSH low Consider if hyperthyroid or Primary hypothyroid
ECG in hypothyroidism
Treatment Algorithm
Management
- Primary hypothyroidism usually has a good prognosis and most people will recover full health following adequate thyroid hormone replacement with levothyroxine (LT4), which is usually needed for life
- Commence Thyroxine 50 mcg od and increase to 100-150 mcg OD. Use 25 mcg dose in elderly or those at risk of IHD
- There is a small number of individuals who require T3 rather than T4
References