Clinical Calcium Homeostasis Flashcards
Main physiological functions of Ca?
- Bone formation
- Synaptic transmission
- Muscle contraction
- Cell division & growth
How does plasma albumin concentration affect the amount of free calcium? By approximately how much?
- Increased albumin decreases free calcium
- Decreased albumin increases free calcium
- Adjust Ca by 0.1mmol/L for each 5g/L reduction in albumin (not 100% sure about that…)
Which gland secretes PTH? From which type of cells?
- Parathyroid glands
- Parathyroid chief cells
What causes the parathyroid gland to secrete PTH?
Calcium sensing receptors (CaSR) on the parathyroid gland stimulate the secretion of PTH when extracellular [Ca] is low
Functions of PTH?
- Resorption of calcium into plasma (osteoclasts & renal reabsorption)
- Secretion of phosphate (PO4)
- Mediates conversion of vitamin D to its active form (calcitriol synthesis)
What plasma calcium concentration suggests hypocalcaemia?
< 2.20 mmol/L
Symptoms usually when < 1.9 mmol/L
What are some symptoms of acute hypocalcaemia?
- Muscle ache
- Paresthesia
- Tetany (neuromuscular irritability)
- Bone pain
- Seizures
- Laryngospasm (spasm of vocal cords)
- Bronchospasm (spasm of bronchial smooth muscle)
What are some cardiac related signs of acute hypocalcaemia?
- Prolonged QT interval
- Hypotension
- Heart failure
- Arrhythmia
- Papilloedema
What are some neuromuscular clinical signs of acute hypocalcaemia?
- Muscle twitching (fasciculations)
- Carpopedal spasm (painful cramps in hands & feet)
- Trousseau’s Sign
- Chovstek’s Sign
What are some signs / symptoms of chronic hypocalcaemia?
- Ectopic calcification (calcification in soft tissue)
- Extrapyramidal signs
- Parkinsonism
- Dementia
- Subcapsular cataracts
- Abnormal dentition / dry skin
What are Trousseau and Chovstek’s signs? What do they suggest?
- Trousseau’s Sign: spasm of the wrist and metacarpal joints after inflating blood pressure cuff around ipsilateral arm for 3 minutes, at above systolic BP
- Chovstek’s sign: twitching of the facial muscles after tapping over the area of the facial nerve
- Both indicate hypocalcaemia
Causes of hypocalcaemia?
- Hypoalbuminaemia (commonest)
- Hypoparathyroidism
- Total thyroidectomy (iatrogenic)
- Severe vitamin D deficiency
- Mg deficiency
- Cytotoxic drugs
- Pancreatitis, rhabdomyolysis, large blood transfusions
Investigations for suspected hypocalcaemia?
Bloods:
- Ca / PO4 / ALP / vitamin D / PTH / Mg / albumin
U&E
(also look for neck scars)
If there is evidence of hypocalcaemia, high PTH and urea and creatinine are also high, what is the likely diagnosis?
Renal failure
If there is evidence of hypocalcaemia, high PTH, normal urea and creatinine, and high vitamin D, what is the likely diagnosis?
Pseudohypoparathyroidism
or Ca deficiency
If there is evidence of hypocalcaemia and low PTH what else should be checked? Possible diagnoses?
Check Magnesium levels
- If normal Mg: Hypoparathyroidism
- If low Mg: Mg deficiency
Causes of hypoparathyroidism?
- Agenesis (DiGeorge symptom)
- Iatrogenic
- Mg deficiency
- Cell resistance to PTH (pseudohypoparathyroidism)
What is Pseudohypoparathyroidism? Symptoms? How will the bloods look?
- When the bone and kidneys are not sensitive to PTH
- Obesity, short stature, shortening of the metacarpals and metatarsals
- Bloods: low Ca, high PO4, high PTH
Treatment of severe hypocalcaemia?
- IV calcium gluconate
management of hypocalcaemia?
- Oral calcium tablets
- Mg / vitamin D supplements if needed (calcitriol if renal impairment instead of vit D)
What blood [Ca] is considered severe hypercalcaemia? What is mild?
> 3.5 mmol/L is severe, needs urgent correction
3.0 - 3.5 is mild hyperglycaemia, may be asymptomatic if it has risen slowly
Causes of hypercalcaemia?
- Bone metastases (malignancy - PTHrp)
- Hyperparathyroidism
- Thyrotoxicosis
- Elevated calcitriol
- High vitamin D
- TB / sarcoidosis
Symptoms of hypercalcaemia?
- Painful bones
- Renal stones
- Abdominal pain
- Depression
(bones, stones, moans, groans) - Polydipsia (thirst)
- Polyuria
Investigations for hypercalcaemia?
Bloods: - PTH - Ca & albumin - Vitamin D - PTH-rp Urine Ca Renal function
Investigations for suspected primary hyperparathyroidism??
- Ca, PTH
- U&Es: check renal function
- Abdominal imaging: renal calculi
- DEXA: osteoporosis
- 24 hour urine collection for calcium: Excl. FHH
- Vitamin D
What is Sestamibi scanning?
- Sestamibi is a small protein which is labeled with the radio-pharmaceutical technetium99, it is injected into the veins of a patient with hyperparathyroidism
- Gets absorbed by the overactive parathyroid gland. normal parathyroid glands are inactive when there is high calcium, they do not take up the radioactive particles
- Gamma camera is placed patient’s neck, shows the overactive gland
What are the indications for surgery for patients with primary hyperparathyroidism?
- High serum calcium
- Renal failure / stones
- < 50 years of age
- Osteoporosis on DEXA
Which pharmaceutical agent causes a fall in PTH? Mechanism?
Cinacalcet: mimics the effect of calcium on the calcium sensing receptor on Chief cells, this leads to a fall in PTH and subsequently calcium levels
What is Familial Hypocalciuric Hypercalcaemia?
- Autosomal dominant disorder of the calcium sensing receptor (CaSR)
- Results in high blood [Ca] and low urine [Ca]
- PTH may be normal or slightly elevated
What hereditary form of cancer is closely related to primary hyperparathyroidism?
- Multiple Endocrine Neoplasia (type 1 & 2)
> 95% of M.E.N. type 1 have hyperparathyroidism, 20-30% for type 2
First line management of hypercalcaemia?
- Hydration
- After rehydration, intravenous bisphosphonates
