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ENDO- OBG > Endocrine Bone Disorders > Flashcards

Endocrine Bone Disorders Flashcards

1
Q

What is the most important vitamin D metabolite?

A

1, 25-dihydroxycholecalciferol (calcitriol)

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2
Q

What is the principle effect of calcitriol?

A

Increase calcium, magnesium and phosphate absorption in the small intestines

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3
Q

What are the other effects of calcitriol?

A

Increased reabsorption of calcium and decreased phosphate reabsorption in the kidneys (via FGF23)

Stimulates osteoclast formation from precursors

Stimulates osteoblasts to make osteoclast-activating factors (OAFs e.g. RANKL)

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4
Q

What does vitamin D deficiency cause? State some symptoms.

A

Lack of bone mineralisation

Softening of bone (can lead to bowing of the legs)

Bone deformities

Bone pain

Severe proximal myopathy

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5
Q

What are the different names for vitamin D deficiency in children and adults?

A

Children – Rickets

Adults – Osteomalacia

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6
Q

State some causes of vitamin D deficiency.

A

Inadequate dietary intake

Lack of sunlight

Receptor defects

Renal failure

Gastrointestinal malabsorptive states

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7
Q

Which step, in vitamin D metabolism, required UV light?

A

The conversion of 7-dehydrocholesterol in the skin to cholecalciferol (vitamin D3) requires UV light

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8
Q

Describe the two hydroxylation reactions in vitamin D metabolism.

A

Cholecalciferol is firstly hydroxylated to form 25-hydroxycholecalciferol in the Liver

It then goes to the kidneys where it undergoes its next hydroxylation (by 1-hydroxylase) to form 1, 25-dihydroxycholecalciferol (calcitriol)

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9
Q

What can stimulate 1-hydroxylase in the kidneys?

A

Parathyroid Hormone (PTH)

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10
Q

How can lack of sunlight cause vitamin D deficiency?

A

It will mean that less 7-dehydrocholesterol is being converted to cholecalciferol

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11
Q

How can liver disease cause vitamin D deficiency?

A

The liver is where the first hydroxylation takes place and where 25-hydroxycholecalciferol is stored so liver disease can interfere with this step in vitamin D metabolism

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12
Q

How can renal failure cause vitamin D deficiency?

A

The second hydroxylation step takes place in the kidneys (via 1-alpha-hydroxylase) so renal failure can interfere with 1-alpha-hydroxylase activity

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13
Q

What is usually measured to gage the level of calcitriol? Whatcondition must be fulfilled for this to be a good measure of calcitriol?

A

25-hydroxycholecalciferol

This is only a good measure in the case of normal renal function

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14
Q

Describe how you would diagnose vitamin D deficiency.

A

Plasma Calcium = LOW

Plasma 25-hydroxycholecalciferol = LOW

Plasma PTH = HIGH (secondary hyperparathyroidism stimulated by the hypocalcaemia)

Plasma Phosphate = LOW

Radiological findings e.g. widened osteoid seams

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15
Q

What would you expect the plasma phosphate level to be in someone with renal failure and why?

A

HIGH – because there is a decrease in plasma excretion via the kidneys

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16
Q

What would you expect the plasma calcium level to be in someone with renal failure and why?

A

LOW – because they are not producing as much calcitriol (due to renalfailure interfering with 1-alpha hydroxylase) so there is less calcium absorption in the small intestines

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17
Q

What are the consequences of hypocalcaemia caused by renal failure?

A

There is a decrease in bone mineralisation and an increase in bone resorption (because of an increase in PTH) leading to osteitis fibrosa cystica

The imbalance in calcium and phosphate can also lead to the formation of salts that can be deposited in extra-skeletal tissue causing extra-skeletal calcification

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18
Q

What can vitamin D excess lead to?

A

Hypercalcaemia and hypercalciuria (due to increased intestinal absorption of calcium)

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19
Q

What can vitamin D excess result from?

A

Excessive treatment with active metabolites of vitamin D, as in patients with chronic renal failure

Granulomatous disease – granulomatous tissue has 1-hydroxylase so it can be a source of ectopic calcitriol

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20
Q

What is Paget’s disease?

A

Very active (increased), localised but disorganised bone metabolism –usually slowly progressive.

There is increased bone breakdown and bone formation.

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21
Q

What is Paget’s disease characterised by histologically?

A

Abnormal, large osteoclasts

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22
Q

State some symptoms of Paget’s disease.

A

Increased vascularity (warmth over affected bone)

Increased osteoblast/osteoclast activity:

  • Initially increased osteoclast activity
  • Followed by increased osteoblast activity (leading to thickening of deformed bone)

Most commonly affected bones are: pelvis, femur, tibia, skull, and spine

Increased incidence of fracture

Bone pain

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23
Q

Describe how you would diagnose Paget’s disease.

A

Plasma calcium = NORMAL

Plasma ALP (alkaline phosphatase) = HIGH

Radiological findings:
 Loss of trabecular (spongy) bone
 Increased bone density
 Deformity

Radioisotope (technetium) scanning can be performed to indicate areas of involvement

24
Q

What are the two components of bone in which 95% of the body’s calcium is stored?

A

Inorganic mineral component –65%
 Stored as calcium hydroxyapatite crystals between the collagen fibrils

Organic (osteoid) component –35%
 Collagen fibres (95%)

25
Q

What is the normal plasma calcium range?

A

2.2-2.6 mmol/L

26
Q

State 2 hormones that increase plasma calcium concentration.

A

Calcitriol

PTH

27
Q

State a hormone that decreases plasma calcium concentration.

A

Calcitonin

28
Q

What are the 2 direct effects of PTH?

A

Increased mobilisation of calcium in bone

Increased calcium reabsorption in the kidneys and stimulation of 1a-hydroxylase

29
Q

What are the 2 direct effects of calcitriol?

A

Increased calcium absorption from the small intestine

Increased mobilisation of calcium in bone

30
Q

What can stimulate PTH release?

A

Hypocalcaemia

31
Q

State 4 signs of hypocalcaemia.

A

Parasthesia

Arrhythmias

Convulsions

Tetany

32
Q

What effect does hypocalcaemia have on excitable tissues?

A

It sensitises excitable tissue –> neuromuscular excitability

33
Q

State 2 clinical signs of neuromuscular irritability due to hypocalcaemia.

A

Chvostek’s Sign
 Tap the facial nerve just below the zygomatic arch
 Positive = twitching of facial muscles

Trousseau’s Sign
 Pump the blood pressure cuff for several minutes
 Induces carpopedal spasm

34
Q

State 4 causes of hypocalcaemia.

A

Hypoparathyroidism (e.g. due to surgery)

Vitamin D deficiency

Pseudohypoparathyroidism

Renal failure (impaired 1-alpha hydroxylase)

35
Q

Describe the effect of hypercalcaemia on neuronal excitability.

A

It reduces neuronal excitability and you get atonal muscles

36
Q

What are the main signs and symptoms of hypercalcaemia?

A

Stones, (Bones), abdominal moans and psychic groans

Stones – renal effects
 Polyuria + polydipsia
 Nephrocalcinosis = deposition of calcium in the kidneys (can cause renal colic)

(Bones- increased fractures due to bone resorption– IF DUE TO ^ PTH)

Abdominal moans – GI effects
 Anorexia, nausea, constipation, pancreatitis, dyspepsia

Psychic groans – CNS effects
 Fatigue, depression, impaired concentration, altered mentation, coma

37
Q

What are the 2 main causes of hypercalcaemia?

A

Primary Hyperparathyroidism (e.g. parathyroid adenoma) Malignancy (e.g. bone tumours/metastases –> increased bone turnover –> increased plasma calcium; tumours can also produce PTH-like peptide)

38
Q

State 2 other causes of hypercalcaemia. (other than primary hyperparathyroidism )

A

Conditions of increased bone turnover (e.g. hyperthyroidism, Paget’s)

Vitamin D excess (rare)

39
Q

Describe how you would differentiate between primary hyperparathyroidism and malignancy causing hypercalcaemia.

A

In primary hyperparathyroidism there is no negative feedback because the parathyroid adenoma will be producing PTH autonomously
 Plasma Calcium = HIGH
 PTH = HIGH

In malignancy, the negative feedback will be intact as it is due to increased bone turnover due to bony metastases
 Plasma Calcium = HIGH
 PTH = LOW

40
Q

Describe the treatment of vitamin D deficiency in the case of normal renal function.

A

Give 25-hydroxy vitamin D

This can be in the form of:
 Ergocalciferol = 25-hydroxy vitamin D2
 Cholecalciferol = 25-hydroxy vitamin D3

41
Q

Describe the treatment of vitamin D deficiency in the case of renal failure.

A

Alfacalcidol = 1-hydroxycholecalciferol

42
Q

What do osteocytes produce?

A

Type 1 collagen and other extracellular matrix components

43
Q

What is RANK ligand?

A

An osteoclast-activating factor – it increases the activation of osteoclasts

It stimulates the maturation of osteoclasts from osteoclast precursors

If there are more mature osteoclasts, you get more bone resorption

44
Q

Define osteoporosis.

A

Having a bone mineral density (BMD) that is 2.5 standard deviations (SD) or more below the average for young healthy adults (usually referred to as a T-score of -2.5 or lower)

BMD is measured using Dual Energy X-ray Absorptiometry (DEXA)

45
Q

State some predisposing conditions for osteoporosis.

A

Post-menopausal oestrogen deficiency

Age-related deficiency of bone homeostasis

Hypogonadism in young men and women

Endocrine conditions (e.g. Cushing’s syndrome, hyperthyroidism, primary hyperparathyroidism)

Iatrogenic (e.g. prolonged use of glucocorticoids, heparin)

46
Q

What are the benefits of oestrogen replacement to prevent osteoporosis in post-menopausal women?

A

It has an anti-resorptive effect in bone and, hence, prevents bone loss

47
Q

What are some cautions and risks of oestrogen replacement?

A

In patients with a uterus (i.e. not had a hysterectomy), you must give additional progestogen to prevent endometrial hyperplasia and reduce the risk of endometrial carcinoma

Risks:
 Breast cancer
 Venous thromboembolism

48
Q

Name 2 selective oestrogen receptor modulators and their effects.

A

Selective oestrogen receptor ANTAGONISTS – Tamoxifen
 Antagonises ERs in the breast
 Oestrogenic activity in bone
 But, oestrogenic activity in uterus, which limits its use in osteoporosis

Selective oestrogen receptor AGONIST – Raloxifene
 Oestrogenic in bone
 Anti-oestrogenic in breast and uterus
 But there is a risk of stroke and venous thromboembolism

49
Q

What are the 1st, 2nd and 3rd line treatments for osteoporosis?

A

Bisphosphonates

Denosumab- binds rankL

Teriparatide

50
Q

Describe how bisphosphonates work.

A

They bind avidly to hydroxyapatite crystals in the bone and are ingested by osteoclasts

They impair the ability of osteoclasts to resorb bone
It also decreases the maturation of osteoclasts and promotes osteoclast apoptosis

51
Q

State some uses of bisphosphonates.

A

Osteoporosis

Malignancy – reduces bony pain

Paget’s disease – reduces bony pain

Severe hypercalcaemic emergency
 I.V. saline to rehydrate
 Then bisphosphonates

52
Q

Describe the pharmacokinetics of bisphosphonates.

A

They are orally active but poorly absorbed
Must be taken on an empty stomach

Accumulates at the site of bone mineralisation and remains a part of the bone until it is resorbed (years)

53
Q

State 4 unwanted actions of bisphosphonates.

A

Oesophagitis

Flu-like symptoms (first dose only)

Osteonecrosis of the jaw (greatest risk in cancer patients receiving IV bisphosphonates)

Atypical fractures (due to over-suppression of bone remodelling)

54
Q

What is denusomab and how often does it need to be given?

A

It s a human monoclonal antibody

It binds to RANKL and inhibits osteoclast formation and activity

It is given subcutaneously every 6-12 months

55
Q

What is teriparatide and how often does it need to be given?

A

Recombinant fragment of PTH

Increases bone resorption and formation – but formation exceeds resorption

Daily subcutaneous injections

EXPENSIVE

ENDO- OBG (17 decks)

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