Parathyroid Flashcards
What is parathyroid hormone (PTH)?
What does it do?
Hormone synthesised and released by the parathyroid gland in response to hypocalaemia.
It increases calcium levels by
- increasing osteoclastic activity which resorbs bone
- increases renal reabsoroption of calcium
- acts on kidneys to convert 20(OH) vitamin D to active calcitriol (1,25 OH vitamin d) which acts on the gut to increase calcium absorption
What is calcitonin?
What does it do?
Hormone released by parafollicular cells of the thyroid gland.
Decreases calcium levels by
- decreasing osteoclastic activity
- inhibiting renal reabsorption of calcium
How is calcium absorbed in the gut?
Generally, poorly.
Calcitriol acts on the gut to increase calcium absorption
Outline the steps involved in vitamin D synthesis and activation.
- Vitamin D enters body from
- Sunlight (converts dehydroxyxholseterol to vitamin D in keratinocytes)
- Diet (fish) - Liver converts vitamin D to 25(OH)-vitamin-D (cholecalciferol)
- Parathyroid hormone acts on kidneys to convert 25(OH)-vitamin-D (cholecalciferol) to 1,25(OH)-vitamin-D (calcitriol)
(calcitriol is active version of vitamin D)
What are the symptoms of acute hypercalcaemia?
Dehyrdation
Confusion
Polyuria
Weakness
What are the ECG findings in hypercalaemia?
Shortened QT interval
Arrhythmia
What are the symptoms are chronic hypercalcaemia?
“stones, bones and psychic mones”
Abdominal pain (renal stones) Bone pain (ostepenia) Depression
What is primary hyperparathyroidism?
Overactive parathyroid gland producing excess PTH
Blood results show:
- Serum Ca: high
- Urinary Ca: normal
- PTH: high
- ALP: normal
- Albumin: normal/low
- Urea: normal/low
Diagnosis?
Primary hyperparathyroidism
What is the treatment of primary hyperparathyroidism?
Usually nothing (incidental)
Parathyroidectomy
if organ dysfunction, young or have very high calcium (>2.85)
What is secondary hyperparathyroidism?
Physiological production of PTH in response to hypocalcaemia.
Blood results show:
- Serum Ca: low
- Urinary Ca: normal
- PTH: high
- ALP: normal
- Albumin: normal
- Urea: normal
Diagnosis?
Secondary hyperparathyroidism
What is tertiary hyperparathyroidism?
Autonomous parathyroid gland occuring after long standing secondary hyperparathyroidism due to chronic hypocalaemia
What can cause tertiary hyperparathyroidism?
Chronic kidney disease
Loss of renal activation of calictriol results chronic hypocalaemia which causes secondary hyperparathyroidism. This causes parathyroid hyperplasia which can progress to tertiary hyperparathyroidism if not treated
How can malignancy cause hypercalcaemia?
Metastatic bone destruction (releases calcium from bones into blood)
Paraneoplasitc production of PTHrp
Osteoclast activating tumours
What would your next step in management be if a patients blood results showed:
- Serum Ca: high
- Urinary Ca: normal
- PTH: low
- ALP: high
- Albumin: normal
- Urea: normal
Imaging to find tumour
Blood results suggest malignant hypercalcaemia
What is familial hypocalcuric hypercalcaemia?
Autosomal dominant condition affecting the calcium sensing receptor causing asymptomatic hypercalcaemia.
Blood results show
- Serum Ca: high
- Urinary Ca: normal
- PTH: high
- ALP: normal
- Albumin: normal
- Urea: normal
Diagnosis?
Familial hypocalcuric hypercalcaemia
Thiazide or loop diuretics cause hypercalcaemia?
Thiazide diuretics cause hypercalcaemia
Blood results show:
- Serum Ca: high
- Urinary Ca: normal
- PTH: normal
- ALP: normal
- Albumin: high
- Urea: high
Diagnosis?
Dehydration
What are the symptoms of hypocalcaemia?
Cramps
Weakness
Paresthesia
What is hypoparathyroidism?
Name 4 causes.
Hypofunction of parathyroid glands resulting in insufficient PTH and hypocalcaemia
Destruction (surgical, autoimmune, chemotherapy)
Parathyoidectomy
DiGeorge syndrome
Hypomagneasaemia
Why does hypomagnesaemia cause hypocalcameia?
Mg required for calcium secretion from cells
How do you treat hypoparathyroidism?
Calcium, vitamin D (+/- magnesium) supplementation
What is pseudohypoparathyroidism?
Low calcium caused by genetic PTH resistance
What gene mutation causes pseudohypoparathyroidism?
GNAS1 gene
How does pseudohypoparathyroidism present?
Obesity, learning difficulty, brachydatyly, McCune Albright syndrome (abnormal bone fibrosis)
Bloods show
- Serum Ca: low
- Urinary Ca: normal
- PTH: low
- ALP: normal
- Albumin: normal
- Urea: normal
Diagnosis?
Hypoparathyroidism
Pseudohypoparathyroidism if phenotype suits e.g. obese, learning difficulties, brachydactyly
What is pseudopseudohypoparathyroidism?
Clinically like pseudohyooparathyroidism (obese, learning difficulties, brachydactyly, abnormal bone) but calcium and pTH normal, i.e. no PTH resistance
Name 5 causes of vitamin D deficiency.
Poor diet Lack of sunlight Malabsoprtion Renal failure Iatrogenic (anticonvulsants)
How does vitamin D deficiency present?
Bone wasting
Dental caries
Muscle wasting
What can vitamin D deficiency cause?
- fractures
- osteopenia
- colonic malignancy
Pancreatiitis causes
a) hypercalcaemia
b) hypocalcaemia
b) hypocalcaemia (dying pancreas takes in lots of calcium)
