Disorders of Calcium and Phosphate Metabolism Flashcards
Where is our main source of calcium from?
Diet
What is the main source of calcium removal?
Kidney
How does vitamin D act on the gut and bone?
- Gut - increase calcium absorption
- Bone - increase resorption of bone, so inc calcium
Which hormones does high calcium inhibit?
PTH and in turn vitamin D
Which hormone actively reduces calcium levels?
Calcitonin - produced by C cells of thyroid, inhibits action of PTH on the bone. Stimulates osteoblasts and increases calcium excretion.
What hormone level change is responsible for hypercalcaemia?
PTH
Biggest causes of hypercalcaemia = high or low PTH
High PTH can cause hypercalcaemia. What is the biggest reason for high PTH?
Vast majority of high PTH cases of hypercalcaemia are due to hyperparathyroidism. Some due to cancer.
What are the causes of low PTH?
- Mainly cancer
- Hypervitaminosis D (exogenous, granulamotous disease, will S)
- Increased bone turnover (acromegaly, thyrotoxicosis)
Describe differences in diagnosing primary, secondary and teritary hyperparathyroidism and how PTH/calcium levels differ
- Primary = PTH high, calcium high
- Secondary = calcium low/normal, PTH high (overcompensating)
- Tertiary = PTH high, calcium high
Teritary only ever diagnosed if there was an obvious previous case of secondary hyperparathyroidism.
Primary hyperparathyroidism is the commonest cause of elevated PTH and calcium levels. What actually causes primary hyperparathyroidism?
- 85% cases are single adenoma
- 15% cases diffuse hyperplasia
< 1% by parathyroid carcinoma
What causes secondary hyperparathyroidism?
- Secondary due to hyperfunctioning of parathyroid glands caused by hypocalcaemia/periph resistance to PTH due to:
- > chronic renal insufficiency
- > calcium malabsorption
- > vitamin D deficiency
- > deranged vitamin D metabolism
What causes tertiary hyperparathyroidism?
Occurs following previous secondary hyperparathyroidism, in which the glandular hyperfunction continue despite correction of the underlying abnormality
- renal transplanatation
One of the hormonal causes of hypercalcaemia of malignancy are metastatic solid tumours. What are the general 4 types?
Lung, breast, kidney, prostate
They enter bone and release calcium into circulation
Name 3 granulomatous diseases
- Sarcoidosis
- Tuberculosis
- Berylliosis
- Coccidioidomycosis
- Histoplasmosis
How do granulomatous diseases cause hypercalcaemia?
They present with big pathogens, so require macrophages to invade - macrophages express 1-a-hydroxylase and over activate vitamin D causing an increase in Vit D -> results in increased calcium!
What do thiazide and loop diuretics do to calcium levels?
Thiazide diuretics block excretion of calcium from the body, so inc calcium in blood whereas loop diuretics decrease calcium in blood.
What does “stones, bones and psychic moans” refer to?
Symptoms of hypercalcaemia
- Kidney stones
- Bone aches
- Confusion, memory loss, dementia, depression
- Constipation, nausea, abd pain, peptic ulcer disease
How is hypercalcaemia investigated / diagnosed?
- Blood levels -> calcium phosphate
- U&E magnesium
- Vitamin D, PTH
- Urinary calcium excretion
- CXR
- ACE levels
- Myeloma screen
In a patient with hyperparathyroidism (high PTH), you want to remove the parathyroid glands. What investigations are carried out?
- DEXA scan to see how much mineral in bone
- sestaMIBI scan to distinguish parathyroid from thyroid gland
- Ultrasound of neck
- USS renal tract
What is the treatment of hypercalcaemia?
- Saline rehydration
- Frusemide
- Pamidronate infusion
- Calcitonin
- Prednisolone
- Dialysis (if calcium 4+)
What is the treatment for hyperparathyroidism?
- Surgery
- Medical - observe, bisphosphonates
- Calcimimetics - cinacalcet (expensive)
What are some conditions associated with low PTH/action hypocalcaemia?
- Hypoparathyroidism
- Pseudo-hypoparathyroidism
- Pseuo-pseudo-hypoparathyroidism
What are the two possible causes for primary hypoparathyroidism?
- Congenital
- Autoimmune
What are the causes of secondary hypoparathyroidism?
- Neck surgery or trauma
- Radioiodine / radiotherapy
- Neonatal
- Hypo and hyper-magnesemia
What causes high PTH hypocalcaemia?
- Vit D deficiency (renal/liver disease)
- Poor dietry Ca
- Malabsorption
- Chelation (where calcium removed eg blood transfusion)
What are symptoms and signs of hypocalcaemia?
- Paresthesias
- Laryngospasm
- Bronchospasm
- Tetany
- Seizures
- Chvostek’s sign
- Trousseau’s sign
- Prolongued QT interval on ECG
What disease does vitamin D deficiency cause?
Osteomalacia
What is severe hypocalcaemia and what is the treatment?
- Carpopedal spasm, fitting, arrhythmia
- Calcium < 1.7 mmol/l
- IV 10ml 10% calcium gluconate diluted in 200ml N saline over 10 mins
What is the treatment for vitamin D deficiency?
- Calcium and vitamin D tablets 800-1000IU daily
- Vitamin D injection 300 000U IM every 6 months
- Alpha calcidol 0.25-1mg daily
What is pseudohypoparathyroidisim?
- Post-receptor defect of PTH receptor, so PTH resistance
- Low calcium
- High phosphate
- Low Vit D hydroxylation
- High PTH
What are characteristics of patients with pseudohypoparathyroidism?
- Body habitus (short, obese, round face)
- Reduced IQ
- Brachydactyly
- Ectopic calcification
