Physiology
Endocrine
Question 42 of 180
Which of the following biochemical patterns is most typical of primary hyperthyroidism:
Answer:
T3, T4 and TSH results:- 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
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 |
