Roles of Calcium
Contraction of skeletal, cardiac and smooth muscle
Control of nerve impulses
- Increases in the level of calcium cause depression of the nervous system
- Decreases in the level of calcium causes excitation of the nervous system
- Increased osteoclast activity
- Decreased excretion of calcium by the kidneys
Signs & Symptoms
Tetany – this most commonly occurs in the hands first, with flexed wrist and fingers together, where it is called carpo-pedal spasm.
- Is some cases, this can be elicited by occluding the brachial artery (e.g. with blood pressure cuff). This is Trousseau’s sign
- Seizures – due to increased excitability of neurons.
- Increased contractility and increased neuron activity
- Peri-oral parasthesia
- Neuromuscular excitability – Chvostek’s sign – tapping over the facial nerve causes facial muscle to twitch
- Cataracts –in chronic hypocalcaemia
- Renal Failure
- PTH deficiency (hypoparathyroidism, e.g. after thyroid surgery, where the parathyroid glands have been removed) – note that is also may be associated with hyperparathyroidism when the low Ca2+ is causing the hyperparathyroidism (secondary hyperparathyroidism)
- Insufficient vitamin D
- Insufficient calcium in diet (rare)
- Excess magnesium in diet (rare)
Signs & Symptoms
- “Bones, stones, groans and psychic moans”
- Depressed nervous system – this can lead to slow reflexes.
- Poly uria / polydipsia
- Decreased QT interval
- Lack of appetite and constipation and vomiting – probably due to decreased contractility of the muscle walls of the GIt.
- Decreased contractility and decreased neuron activity
- Formation of calcium phosphate crystals at very high levels of Ca2+ in the blood
- Decreased QT interval on ECG
Primary and tertiary hyperparathyroidism (PTH excess)
Bone metastases - These causes can be differentiated by looking at:
- ↓ albumin
- ↓ chloride
- ↓ potassium
- If these three factors are present, then the cause is likely metastatic
- Saline 0.9% IV
- Correct any hypokalaemia and hypomagnesia. This will reduce symptoms and increase renal excretion of calcium
- Bisphosphonate – e.g. pamidronate – these reduce osteoclast activity. Give a single dose. Will lower blood calcium over 2-3day period
- Diuretics may be considered (e.g. Frusemide). Thiazide diuretics should not be used.