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Yr 4 - OSCE Stations > Bone Profile Interpretation > Flashcards

Bone Profile Interpretation Flashcards

1
Q

What does a bone profile involve?

A

1) Serum calcium

2) Serum phosphate

3) Serum albumin

4) ALP

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2
Q

What are the 3 main processes that determine serum calcium?

A

1) Intestinal absorption

2) Renal excretion

3) Bone turnover

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3
Q

Where is calcium absorbed?

A

Small intestine

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4
Q

What regulates the intestinal absorption of calcium?

A

Vitamin D

Vitamin D deficiency leads to decreased calcium absorption from the gut.

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5
Q

What regulates the renal excretion of calcium?

A

PTH

Increased PTH levels lead to decreased levels of renal calcium excretion.

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6
Q

Calcium is released from old bone and taken up by new bone.

What is this process regulated by/

A

PTH

Increased PTH levels lead to increased calcium resorption from the bone into the bloodstream.

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7
Q

What 3 ways does PTH increase serum calcium?

A

1) Decreases renal excretion of calcium

2) Increases calcium resorption from bone

3) Indirectly increases calcium levels by increasing Vitamin D activation in the kidney

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8
Q

Give some causes of hypercalcaemia

A

1) Excessive PTH:
- 1ary hyperparathyroidism
- 3ary hyperparathyroidism
- ectopic PTH secretion (rare)

2) Malignancy:
- myeloma
- bony metastases
- paraneoplastic syndromes

3) Excessive vitamin D:
- exogenous excess
- granulomatous disease (e.g. sarcoidosis)

4) Excessive calcium intake: ‘milk-alkali’ syndrome

5) Renal disease (severe AKI)

6) Drugs:
- thiazide diuretics
- lithium

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9
Q

What 2 drugs can notably cause hypercalcaemia?

A

1) lithium
2) thiazide diuretics

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10
Q

What are over 90% of cases of hypercalcaemia due to? (2)?

A

1) 1ary hyperparathyroidism

2) Malignancy

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11
Q

What is the key next step in assessing hypercalcaemia?

A

Request a PTH

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12
Q

PTH levels in malignancy vs 1ary hyperparathyroidism?

A

Malignancy –> suppressed due to negative feedback

1ary hyperparathyroidisim –> raised

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13
Q

What are some features of hypercalcaemia?

A

Bones: bone pain, pathological fractures

Renal stones: renal colic

Abdo groans: abdominal pain, vomiting, constipation, pancreatitis

Psychic moans: confusion, hallucination, lethargy, depression

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14
Q

What will an ECG classically show in hypercalcaemia?

A

Shortened QT interval –> can progress to cause complete AV nodal block and cardiac arrest.

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15
Q

What does the initial management of hypercalcaemia involve?

A

Aggressive IV fluid rehydration (saline)

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16
Q

What may be required for treatment of hypercalcemia refractory to rehydration?

A

Bisphosphonates

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17
Q

Give some causes of hypocalcaemia?

A

1) PTH deficiency:
- 1ary hypoparathyroidism (autoimmune)
- parathyroid damage (post thyroid/parathyroid surgery or post neck irradiation)
- severe hypomagnesemia (impairs PTH secretion)

2) Vit D deficiency

3) Acute pancreatitis

4) Drugs: bisphosphonates, calcitonin

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18
Q

What 2 drugs can notably cause hypocalcaemia?

A

1) Bisphosphonates

2) Calcitonin

19
Q

Features of hypocalcaemia?

A
  • Muscle weakness/cramps
  • Muscle tetany/spasm
  • Perioral paraesthesia
  • Psychological disturbance
  • Seizures
20
Q

What are 2 pathognomonic clinical signs of hypocalcaemia related to muscle tetany?

A

1) Trosseau’s sign

2) Chvostek’s sign

21
Q

What is Trosseau’s sign?

A

Occlusion of the brachial artery (e.g. with a BP cuff) leads to involuntary contraction of the hand/wrist.

22
Q

What is Chvostek’s sign?

A

Tapping over the facial nerve causes contraction of facial nerves

23
Q

What may ECG show in hypocalcaemia?

A

QT prolongation –> can progress to torsades de pointes and cardiac arrest.

24
Q

Mx of hypocalcaemia?

A

Calcium replacement.

Mild/mod symptoms –> oral calcium (e.g. calcium carbonate)

Severe/ECG changes –> IV calcium gluconate

25
Q

Impact of PTH on phosphate?

A

Increased PTH causes increases renal excretion of phosphate (i.e. lowers phosphate levels).

26
Q

What are some causes of hyperphosphataemia?

A

1) Renal impairment

2) Acute phosphate load:
- tumour lysis syndrome
- rhabdomyolysis
- exogenous phosphate-containing laxatives

3) Excessive phosphate resorption:
- hypoparathyroidism
- drugs (e.g. bisphosphonates)

27
Q

What is the most common cause of hyperphosphatemia?

A

CKD –> phosphate excretion markedly impaired as the eGFR falls below 25

28
Q

Mx of acute hyperphosphatemia?

A

Acute hyperphosphatemia will generally self-resolve within 6-12 hours if renal function is normal and may need no specific treatment.

IV saline can be used to help accelerate phosphate excretion.

29
Q

Mx of chronic hyperphosphatemia (e.g. due to CKD)?

A

Treatment is focused on decreasing phosphate intake (dietary modification) and absorption (phosphate-binding medications).

30
Q

What are some causes of hypophosphataemia?

A

1) Decreased absorption:
- inadequate intake
- medications (e.g. antacids or phosphate binders)
- chronic diarrhoea

2) Increased urinary excretion:
- hyperparathyroidism
- vitamin D deficiency

3) Internal redistribution:
- refeeding syndrome (phosphate shifts intracellularly)
- hungry-bone syndrome (increased calcium and phosphate deposition in bone post parathyroidectomy)

3) Renal replacement therapy

31
Q

Mx of hypophosphataemia?

A

oral phosphate replacement

32
Q

What are the 2 key functions of albumin?

A

1) Maintaining plasma oncotic pressure.

2) Transporting various substances in the bloodstream, such as cations, fatty acids and exogenous drugs.

33
Q

Give 2 causes of hypoalbuminaemia

A

1) Decreased albumin production:
- malnutrition
- severe liver disease

2) Increased albumin loss:
- protein-losing enteropathies
- nephrotic syndrome

34
Q

Raised ALP is often suggestive of what 2 things?

A

1) Cholestasis

2) Bone disease

35
Q

What is cholestasis?

A

an interruption in bile flow from hepatocytes to the gut

36
Q

How can cholestasis and bone disease (in the context of a raised ALP) be differentiated?

A

Gamma-glutamyltransferase (GGT)

1) Rise in ALP + normal GGT –> increased bone turnover

2) Rise in ALP + GGT rise –> cholestasis

37
Q

What are 4 causes of an isolated ALP rise (i.e. normal GGT)?

A

1) Paget’s disease of the bone

2) Bony metastases

3) Osteomalacia (Vitamin D deficiency)

4) Healing fractures

38
Q

In what 2 situations is ALP physiologically raised?

A

1) children & adolescents

2) pregnancy (3rd trimester)

39
Q

Calcium, phosphate, ALP and PTH levels in 1ary hyperparathyroidism?

A

Calcium –> raised

Phosphate –> low

ALP –> raised

PTH –> raised

40
Q

Calcium, phosphate, ALP and PTH levels in bony mets?

A

Calcium –> raised

Phosphate –> normal

ALP –> raised

PTH –> low

41
Q

Calcium, phosphate, ALP and PTH levels in Paget’s disease?

A

Calcium –> normal

Phosphate –> normal

ALP –> raised

PTH –> normal

Note –> Paget’s disease has an ISOLATED rise in ALP.

42
Q

Calcium, phosphate, ALP and PTH levels in osteoporosis?

A

All NORMAL

43
Q

Calcium, phosphate, ALP and PTH levels in osteomalacia?

A

Calcium –> normal/low

Phosphate –> normal/low

ALP –> raised

PTH –> normal/high

44
Q
A

Yr 4 - OSCE Stations (17 decks)

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