Physiology
Endocrine
Question 105 of 180
Which of the following is the most common cause of hyperthyroidism:
Answer:
Graves disease is the most common cause of hyperthyroidism.Graves disease is an autoimmune disease in which autoantibodies against TSH receptors are produced. These antibodies bind to and stimulate these TSH receptors leading to an excess production of thyroid hormones.Hyperthyroidism
Physiology / Endocrine / Thyroid Function
Last Updated: 21st April 2019
The overproduction of T3 and T4 leads to hyperthyroidism.
Causes
- Graves disease (autoimmune thyroid disease)
- Results from the production of TSH receptor stimulating antibodies
- Most common cause of hyperthyroidism
- Nodular thyroid disease
- Results from autonomous secretion of T3 and/or T4, either from a solitary toxic nodule or numerous nodules within a multinodular goitre
- Second most common cause of hyperthyroidism
- Thyroiditis (e.g. viral, postpartum, drugs)
- Results from inflammation of the thyroid gland causing a destructive release of thyroxine
- Less common
Clinical Features
- Symptoms
- Weight loss (often with increase appetite)
- Insomnia, irritability and anxiety
- Heat intolerance
- Palpitations
- Tremor
- Pruritus
- Increased bowel frequency and loose motions
- Menstrual disturbance
- Reduced fertility
- Signs
- General
- Resting tachycardia (sinus rhythm or AF)
- Warm peripheries
- Proximal myopathy
- Resting tremor
- Hyperreflexia
- Lid lag
- Hypertension and flow murmur
- Agitation and restlessness
- Goitre
- Graves disease
- Thyroid eye disease (in order of increasing severity)
- Dry/gritty eyes
- Eyelid swelling, chemosis and periorbital oedema
- Proptosis and lid retraction
- Diplopia
- Exposure keratopathy and compressive optic neuropathy
- Skin changes
- Pretibial myxoedema
- Thyroid acropachy
- Thyroid eye disease (in order of increasing severity)
- General
![Proptosis and Lid Retraction in Graves Disease By Jonathan Trobe, M.D. - University of Michigan Kellogg Eye Center (The Eyes Have It) [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2018/08/Proptosis_and_lid_retraction_from_Graves_Disease.jpg)
Proptosis and Lid Retraction in Graves Disease. (Image by Jonathan Trobe, M.D. - University of Michigan Kellogg Eye Center (The Eyes Have It) [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons)
![Pretibial myxoedema and thyroid acropachy By Herbert L. Fred, MD and Hendrik A. van Dijk (http://cnx.org/content/m14924/latest/) [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons](https://primary-cdn.frcemsuccess.com/wp-content/uploads/2018/08/Myxedema.jpg)
Thyroid Acropachy and Pretibial Myxoedema. (Image by Herbert L. Fred, MD and Hendrik A. van Dijk (http://cnx.org/content/m14924/latest/) [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons)
Investigations
- T3, T4 and TSH
- Elevated T4 and T3 with suppressed TSH = Primary hyperthyroidism
- Elevated T3 with suppressed TSH = T3 toxicosis
- Normal T4 and T3 with suppressed TSH = Subclinical hyperthyroidism
- Elevated T4 and T3 with non-suppressed TSH = Consider assay interference or secondary hyperthyroidism e.g. TSHoma or thyroid hormone resistance
- Thyroid antibodies (e.g. thyroid peroxidase (TPO) and TSH receptor stimulating antibodies)
- Thyroid ultrasound scan
- Nuclear imaging (technetium or iodine uptake isotope scan)
Management
- Anti-thyroid medication
- Thionamides (carbimazole and propylthiouracil) reduce synthesis of T3 and T4 and can be used in a 'titration' or 'block and replace' regimen
- Beta-blockers can be used to control symptoms until patient becomes euthyroid
- Definitive treatment
- Surgery
- Radioactive iodine (RAI)
Thyroid Storm
This is a rare medical emergency that presents with high output cardiac failure and extreme agitation. It has a high mortality and requires high dependency care.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
