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Endocrine > Disorders of Calcium Homeostasis > Flashcards

Disorders of Calcium Homeostasis Flashcards

1
Q

What occurs in calcium metabolism?

A

Vitamin D3 is hydroxylated in the liver to calcidiol, which is turned into calcitriol in the kidneys

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2
Q

Where is calcitriol transported to?

A

Small intestines = increases absorption of dietary calcium

Bone = releases calcium and phosphates

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3
Q

What do the responses of the small intestine and bone to calcitriol do?

A

Increases serum calcium

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4
Q

What is the role of the parathyroid glands in calcium metabolism?

A

Sense low serum calcium and increase PTH secretion

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5
Q

What is the role of PTH in calcium metabolism?

A

Acts on kidneys to increase calcitriol formation and decrease calcium excretion, also increases activity of bone

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6
Q

What senses serum calcium levels in the parathyroid gland?

A

Calcium-sensing receptor (C ASR) = G-protein coupled receptor involved in regulation of extracellular calcium homeostasis

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7
Q

What are the general symptoms of hypercalcaemia?

A

Bone pain, gallstones, abdominal pain, psychiatric complaints

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8
Q

What are the symptoms of acute hypercalcaemia?

A

Thirst, dehydration, confusion, polyuria

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9
Q

What are the symptoms of chronic hypercalcaemia

A

Myopathy, fractures, osteoporosis, depression, hypertension, pancreatitis, DU, renal calculi

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10
Q

What are some causes of hypercalcaemia?

A

Primary hyperparathyroidism, malignancy, vitamin D and thiazides, TB, sarcoidosis, familial hypocalciuric hypercalcaemia, high turnover, bedridden, thyrotoxic, Paget’s

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11
Q

How is primary hyperparathyroidism diagnosed?

A

Raised serum calcium
Raised serum PTH (or inappropriately normal)
Increased urine calcium excretion

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12
Q

How does hypercalcaemia arise from malignancy?

A

Metastatic bone destruction, PTHrp from solid tumours, osteoclast activating factors

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13
Q

How is hypercalcaemia from malignancy diagnosed?

A

Raised calcium and alkaline phosphatase, x-ray, CT, MRI, isotope bone scan

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14
Q

How should acute hypercalcaemia be treated?

A

Rehydrate with 0.9% saline (4-6L in 24hrs)
Consider loop diuretics once rehydrated
Rarely salmon calcitonin
Chemotherapy may reduce calcium in malignancy

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15
Q

How are bisphosphonates used to treat acute hypercalcaemia?

A

Single dose will lower calcium over 2-3 days, maximal effect at 1 week

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16
Q

When are steroids used to treat acute hypercalcaemia?

A

In sarcoidosis = 40-60mg prednisolone per day

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17
Q

How is primary hyperparathyroidism managed?

A

Surgery

Cinacalcet = calcium mimetic, useful if unfit for surgery

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18
Q

What are the indications for a parathyroidectomy?

A

End organ damage
Very high calcium (>2.85mmol/L)
Age <50
eGFR <60mL/min

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19
Q

What are some examples of end organ damage that would qualify a patient for a parathyroidectomy?

A

Bone disease = osteitis fibrosa et cystica, brown tumours

Gastric ulcers, renal stones, osteoporosis

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20
Q

What is primary hyperparathyroidism?

A

Primary overactivity of parathyroid gland, high calcium and PTH

21
Q

What is secondary hyperparathyroidism?

A

Physiological response to low calcium or vitamin D, low calcium, high PTH

22
Q

What is tertiary hyperparathyroidism?

A

Parathyroid becomes autonomous after many years of overactivity, high calcium and PTH

23
Q

What are some genetic syndromes associated with hypercalcaemia?

A

MEN1/2 and familial isolated hyperparathyroidism

24
Q

What are some features of MEN1/2?

A

Will almost always have developed a parathyroid adenoma with hypercalcaemia at a young age

25
Q

What are some features of familial isolated hyperparathyroidism?

A

Adenoma occurs as in primary hyperparathyroidism

26
Q

What are some features of familial hypocalciuric hypercalcaemia?

A

Autosomal dominant, deactivating mutation in calcium sensing receptor, usually benign or asymptomatic

27
Q

How is hypocalciuric hypercalcaemia diagnosed?

A

Mild hypercalcaemia, reduced urine calcium excretion, PTH may by marginally elevated, genetic screening

28
Q

What are some MSK symptoms of hypocalcaemia?

A

Paraesthesia (fingers, toes, perioral), muscle cramps, tetany, muscle weakness, fatigue, fits, broncho/laryngospasm

29
Q

What are some signs of hypocalcaemia?

A

Chovstek’s sign (tapping over facial nerve), Trousseau sign (carpopedal spasm), QT prolongation on ECG

30
Q

How is acute hypocalcaemia treated?

A

IV calcium gluconate 10ml, 10% over 10mins (in 50ml saline/dextrose)
Infusion = 10ml 10% in 100ml infusate, at 5ml/h

31
Q

What are some causes of hypoparathyroidism?

A

Congenital absence = DiGeorge syndrome
Destruction = surgery, radiotherapy, malignancy
Autoimmune, hypomagnesaemia, idiopathic

32
Q

What is the long term management of hypocalcaemia?

A

Calcium supplement = >1-2g per day
Vitamin D tablets = 1 alphacalcidol 0.5-1mcg
Depot injection = cholecalciferol 300000 units every 6 months

33
Q

Why is PTH release inhibited in hypomagnesaemia?

A

Calcium release from cells is dependent on magnesium

34
Q

What are some features of hypomagnesaemia?

A

Intracellular calcium is high, skeletal and muscle receptors are less sensitive to PTH

35
Q

What are some causes of hypomagnesaemia?

A

Alcohol, thiazides, PPI, GI illness, pancreatitis, malabsorption

36
Q

What causes pseudohypoparathyroidism?

A

Genetic defect = dysfunction of G-protein (Gs alpha subunit), mutation in GNAS gene

37
Q

What are some features of pseudohypoparathyroidism?

A

Low calcium, high PTH (due to PTH resistance)

38
Q

What can occur due to pseudohypoparathyroidism?

A

Bone abnormalities (McCune Albright), obesity, subcutaneous calcification, learning disability, brachdactyly (4th metacarpal)

39
Q

What is pseudo-pseudohypoparathyroidism?

A

Albright’s hereditary osteodystrophy but no alteration in PTH action so normal calcium levels

40
Q

What can cause vitamin D deficiency?

A

Dietary deficiency, chronic renal failure, lack of sunlight, drugs (e.g anticonvulsants)
Malabsorption = gastric surgery, coeliac, liver disease, pancreatic failure

41
Q

What are some features of osteomalacia?

A

Low calcium, muscle wasting (proximal myopathy), dental defects (caries, enamel), bone tenderness, fractures, rib and leg deformity

42
Q

What can chronic renal disease cause?

A

Vitamin D deficiency and secondary hyperparathyroidism

43
Q

What are some features of chronic renal disease?

A

May have high 25-OH vit D, need to check 1-25 OH vit D, titrate treatment to PTH levels, don’t forget phosphate binders

44
Q

What are the long term consequences of vitamin D deficiency?

A

Demineralisation of bone, fractures, rickets, osetomalacia, malignancy (especially colon), heart disease, diabetes

45
Q

What is the treatment of chronic vitamin D deficiency?

A

Vitamin D3 tablets (400-800lU per day after loading with 3200iU per day for 12 weeks), Calcitrol, Alfacalcidol
Combined calcium and vitamin D (Adcal D3)

46
Q

What causes vitamin D-resistant rickets?

A

X-linked hypophosphataemia = variable penetration, PHEX or FGF23 gene mutation

47
Q

What is the role of FGF23?

A

Regulates phosphate levels in plasma and is secreted by osteocytes in response to calcitriol

48
Q

What are some features of vitamin D-resistant rickets?

A

Low phosphate, high vitamin D = treat with phosphate and vitamin D supplements +/- surgery

49
Q

What is the most important test to do for calcium disorders?

A

PTH

Endocrine (42 decks)

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