Parathyroid Hormone and Calcium Homeostasis

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Questions and Answers

What does a family history of hypercalcaemia raise the possibility of?

Secondary hyperparathyroidism

Primary hyperparathyroidism

Milk-alkali syndrome

Familial hypocalciuric hypercalcemia (correct)

What do high plasma phosphate and alkaline phosphatase levels accompanied by renal impairment suggest?

Familial hypocalciuric hypercalcemia

Primary hyperparathyroidism

Secondary hyperparathyroidism

Tertiary hyperparathyroidism (correct)

What can hypercalcaemia cause that may result in hyperuricaemia and hyperchloraemia?

Nephrocalcinosis (correct)

Renal tubular impairment

Hyperparathyroidism

Renal calculi

What is the net effect of prolonged exposure of bone to high levels of PTH?

Mobilisation of calcium into the extracellular fluid Signup and view all the answers

What is the effect of pulsatile release of PTH on bone?

Causes net bone gain Signup and view all the answers

What is the most common cause of hypercalcaemia?

Malignancy Signup and view all the answers

What are the classic symptoms associated with primary hyperparathyroidism?

Bones, stones and abdominal groans Signup and view all the answers

What is the role of parathyroid hormone (PTH) in regulating calcium and phosphate homeostasis?

Enhancing calcium absorption from the gut by promoting the conversion of 25-hydroxyvitamin D to the active metabolite Signup and view all the answers

How do the parathyroid chief cells respond to changes in calcium concentrations?

By directly interacting with the calcium-sensing receptor located on the cell surface Signup and view all the answers

What happens to PTH secretion when serum ionized calcium levels fall?

It rises Signup and view all the answers

What is the main function of PTH on the skeleton?

Increasing osteoclastic bone resorption and bone formation Signup and view all the answers

What is the most likely diagnosis if PTH levels are detectable or elevated in the presence of hypercalcaemia?

Primary hyperparathyroidism Signup and view all the answers

What does a biochemical presentation similar to primary hyperparathyroidism with low urinary calcium excretion indicate?

Familial hypocalciuric hypercalcemia Signup and view all the answers

What condition is suggested by high plasma phosphate and alkaline phosphatase levels accompanied by renal impairment?

Tertiary hyperparathyroidism Signup and view all the answers

What is the recommended initial medical management for severe hypercalcaemia?

IV 0.9% saline 2–4 L/day Signup and view all the answers

What is the duration of action of calcitonin in the treatment of hypercalcaemia?

4 weeks Signup and view all the answers

In the medical management of severe hypercalcaemia, what is the alternative option for patients with refractory hypercalcaemia if zoledronic acid is not effective?

Denosumab initial dose 60 mg SC Signup and view all the answers

What is the most common cause of hypocalcaemia?

Low serum albumin with normal ionised calcium concentration Signup and view all the answers

How does magnesium depletion cause hypocalcaemia?

By impairing the ability of parathyroid glands to secrete PTH Signup and view all the answers

What is the effect of hypomagnesaemia on serum phosphate levels?

Causes variable serum phosphate levels Signup and view all the answers

How should calcium be adjusted in the presence of hypoalbuminaemia?

Increase by 0.02 mmol/L for every 1 g/L reduction in albumin below 40 g/L Signup and view all the answers

What is the characteristic phenotype associated with pseudohypoparathyroidism?

High serum phosphate and alkaline phosphatase levels accompanied by renal impairment Signup and view all the answers

What is the characteristic triad of symptoms seen in children with tetany?

Carpopedal spasm, stridor, and convulsions Signup and view all the answers

What is the latent tetany detected by eliciting Trousseau’s sign?

Inflation of a sphygmomanometer cuff on the upper arm followed by carpal spasm within 3 minutes Signup and view all the answers

What may prolonged hypocalcaemia and hyperphosphataemia cause in association with hypoparathyroidism?

Calciﬁcation of the basal ganglia, grand mal epilepsy, and psychosis Signup and view all the answers

What is the recommended initial management for severe hypocalcaemia?

$10–20 mL 10% calcium gluconate IV over 10–20 mins Signup and view all the answers

What may hypocalcaemia associated with hypophosphataemia cause in children and adults?

Rickets in children and osteomalacia in adults Signup and view all the answers

Study Notes

Overview of Hypercalcaemia in Cancer

Hypercalcaemia is the most prevalent metabolic disorder in cancer patients, affecting up to 20%.
Highest incidence occurs in myeloma and breast cancer, reaching approximately 40%.
Intermediate incidence found in non-small cell lung cancer; uncommon in colon, prostate, and small cell lung cancers.

Mechanisms of Hypercalcaemia

Overproduction of PTHrP (Parathyroid Hormone-related Peptide) accounts for around 80% of cases.
PTHrP binds to the PTH receptor, leading to increased serum calcium through:
- Stimulating osteoclastic bone resorption.
- Enhancing renal tubular reabsorption of calcium.
Direct invasion of bone metastases contributes to about 20% of hypercalcaemia cases.
Ectopic secretion of PTH is rare.

Clinical Features

Symptoms are often non-specific and can resemble those of the underlying cancer.
Common symptoms include:
- Drowsiness and delirium.
- Nausea and vomiting.
- Constipation.
- Increased urination (polyuria) and thirst (polydipsia).
- Dehydration.

Diagnosis and Management

Diagnosis involves measuring serum total calcium, adjusting for albumin levels.
Correcting for hypoalbuminaemia is crucial as it is common in cancer, affecting ionised calcium calculations.
Initial treatment includes:
- Administration of intravenous 0.9% saline for renal function improvement and increased urinary calcium excretion.
- Often leads to clinical improvement.
Concurrently, intravenous bisphosphonates are used to inhibit bone resorption.

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Description

Explore the role of parathyroid hormone (PTH) in regulating calcium and phosphate levels, as well as its impact on vitamin D metabolism. Learn about the consequences of altered PTH function in gut and renal disease, metabolic bone diseases, disorders of the parathyroid glands, hypercalcemia, and hypocalcemia.