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eLCRS - 머크 > 2 Metabolic Bone disease: Biochemistry + Radiology > Flashcards

2 Metabolic Bone disease: Biochemistry + Radiology Flashcards

1
Q

What is the normal range for Plasma [Ca2+] ?

A

2.15 – 2.56 mMol/L

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2
Q

What are the major types of imaging when looking at bone ?

A

Looking at density:

  • X-rays
  • CT
  • Bone densitometry
  • MRI – measure biochemical composition
  • Radionuclide bone scans – measures bone turnover, tracer goes to areas of increased osteoblast activity e.g. joints, fractures, tumour site
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3
Q

Why is imaging useful ?

A
  • It reveal structural failures e.g. fractures + ligamentous injuries
  • It serves as proxy to metabolic dysfunction
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4
Q

What are radiological sings of osteoporosis?

A
  1. Loss of cortical bone (outer white lining)/thinning of cortex
  2. Loss of trabeculae
  3. Insufficiency fractures
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5
Q

what are insufficiency fractures?

A

stress fractures due to normal stress on abnormal bones

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6
Q

what are common sites of insufficiency fractures?

A
  • sacrum
  • underside of femoral neck, - vertebral bodies,
  • pubic rami
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7
Q

What would you see in the imaging of insufficiency fractures?

A

a) XR/CT =
1. Initially normal
2. Can get periosteal reaction + callus
3. More commonly increased sclerosis around fracture lines

b) MRI: bone oedema, i.e. low signal on T1, high signal on T2 and STIR
c) Bone scan: increased osteoblastic activity i.e. increased uptake

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8
Q

when diagnosing osteoporosis by DEXA:

you get T-score:
Z score:

what do these scores mean?

A

Gives T-score: in relation to white adult pre-menopausal females

o And Z-score where ref. database is age + sex matched

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9
Q

o T score:
- 1.5 to -2.5 = _______

< -2.5 =

A

o T score:
- 1.5 to -2.5 = osteopenia,

< -2.5 = osteoporosis

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10
Q

What are radiological signs of osteomalacia?

A
  • Too much un-mineralised osteoid may develop Looser’s zone
  • May cause compensatory secondary hyperparathyroidism –> if calcium stays low
  • Radiology depends on age + closure of growth plate
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11
Q

What is meant by Looser’s Zone?

when might it appear?

A

looser’s zone = type of insufficiency fractures/psuedofractures at high tensile stress areas

  • E.g. medial proximal femur, lateral scapula, pubic rami, posterior proximal ulna, ribs

= radiological sings of osteomalacia

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12
Q

What do Looser’s zone look like?

A

o Typically, look like short, lucent lines w irregular sclerotic margins (below)

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13
Q

Osteomalacia Adult patient with mature skeleton (closed growth plate):

what are signs you might observe?

A
  • Osteopenia
  • Looser’s zones
  • Codfish vertebrae = biconcave bone appearance (sup/inf) in both osteoporosis + osteomalacia
  • Bending deformities
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14
Q

Osteomalacia Child patient with unclosed growth plate

what are signs you might observe?

A

same as adult

–> but changes would be centered mainly on growth plates

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15
Q

What are radiological signs of rickets ?

A
  1. Indistinct/frayed metaphyseal margin
  2. Widened growth plate w/o calcification
  3. Cupping/splaying metaphyses due to increased weight bearing on soft bone
  4. Enlargement of anterior ribs
  5. Osteopenia
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16
Q

What are radiological signs of hyperparathyroidism ?

A

Primary:
- see bone resorption

Secondary (e.g. due to CKD):
- see bone resorption AND increased density

Bone resorption common sites:
o Subperiosteal
o Subchondral
o Intracortical (within bone)
o Brown Tumours, large lytic bone lesion (hyperparathyroidism, cancer, etc.)
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17
Q

Renal Osteodystrophy = special type of primary / secondary hyperparathyroidism

A

Renal Osteodystrophy = special type of primary hyperparathyroidism

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18
Q

What are radiological signs of renal osteodystrophy?

A
  • Osteomalacia + osteoporosis
  • May cause secondary hyperparathyroidism, leading to:
  • -> Subperiosteal erosions, brown tumours

–> Sclerosis – vertebral endplates giving rugger jersey spine = vertebrae have thick top and bottom but less dense centre

–> Soft tissue calcification (e.g. around vessels or cartilages)

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19
Q

What are radiological signs of paget’s disease?

A
  1. Cortical thickening
  2. Bone expansion (usually doesn’t cross joint)
  3. Coarsening of trabeculae
  4. Osteolytic, osteosclerotic, and mixed lesions
  5. Osteoporosis circumscripta – see lucent (pale) spaces, holes in bones
    * Paget’s tends to affect 1 BONE, and probably not adjacent bones
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20
Q

cancellous bone metabolically active / inactive

A

cancellous bone metabolically active

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21
Q

calcium you take in about ______ /day

A

1 g /day

22
Q

how many % of Ca is protein bound?

how many % of Ca is free ionized ?

A

how many % of Ca is protein bound?
46%

how many % of Ca is free ionized ?
7%

23
Q

decrease in Ca2+
[describe what happens]

PTH :
in bone:
in kidney :

A

PTH : increases
in bone: increase resorption
in kidney : increases Ca2+ absorption (via TRPV5/6 channel in DCT)

24
Q 
What is PTH 
- how many a.acid 
- dependent on: 
T1/2 = 
PTH receptor is also activated by =
A
  • 84 amino acid peptide
  • Mg dependent
  • T1/2 = 8 min
  • PTH receptor = activated also by PTH rP (high during breast feeding)
25
Q

note: PTH has receptor on osteoblast

which signal through RANKL - to osteoclast to differentiate and absorb bone

A

-

26
Q

Primary hyperparathyroidism =

  • more common in females
  • primarily due to adenoma
A

-

27
Q

how would you diagnose primary HPT

A
  • increase in ca2+ with PTH levels elevated / non suppressed (or in upper half of normal range)
28
Q

what re clinical features of primary HPT

A
  • symptoms are usually due to high ca:
  • thirst
  • poly uria
  • tiredness
  • fatigue
  • muscle weakness

stones, abdominal moans, psychic groans

29
Q

How does high serum calcium cause diuresis?

A

high serum calcium causes diuresis
ca receptors on cell –> switches off K+ recycling in ascending limb
which causes diuresis

–> increase dehydration

30
Q

chronically elevated PTH causes increased / decreases cortical bone resorption

  • increased / decreased bone turnover
A

chronically elevated PTH causes increased cortical bone resorption

  • increased bone turnover
31
Q

When would surgery be recommended for Primary HPT?

A
  • serum Ca2+ > 0.25mmol/L
  • high 24hr urine Ca2= > 10mmol
  • reduced creatinine clearance
32
Q

what biochemicals would you find in primary hyperparathyrodism?

A
33
Q

describe how Vit D is metabolized by the liver and kidney

A

7 dehydrocholesterol –> cholecalciferol (via UV)
cholecalciferol –> 25 -cholecalciferol

25 -cholecalciferol

34
Q

note:

most absorption of vit d in gut = paracellular

A

-

35
Q

what is Rickets

A

inadequate Vit D activity leads to defective mineralisation of the cartilaginous growth

36
Q

whatclincal features can hypocalcemia cause ?

A
  • chvostek’s sign
  • bronchospasm
  • Trousseau’s sign
  • cardiac failure
37
Q

What could be some causes of rickets/ osteomalacia?

A
  • dietary
  • drugs
  • small bowel malabsorption
  • chronic renal failure
  • rare hereditary conditions
38
Q

What could be some causes of rickets/ osteomalacia?

A
  • dietary
  • drugs
  • small bowel malabsorption
  • chronic renal failure
  • rare hereditary conditions
39
Q

biochemistry in rickets/ osteomalacia

serum [Ca2+ ] =
serum [PO43- ] =
serum [Alk Phos ] =
serum [24(OH)vit D ] =

A

serum [Ca2+ ] low
serum [PO43- ] low
serum [Alk Phos ] High
serum [24(OH)vit D ] low

40
Q

note:

FGF23 + PTH hormones causes loss of phosphate
NPT2a + NPT2c (channels) = in luminal membrane
wastes phosphate out of kidney

A

-

41
Q

excess FGF23 can cause ____________

A

rickets / osteomalacia

–> increased renal phosphate wasting

42
Q

when kidney proximal tubule damaged (falcon syndrome)
–> causes phosphaturia

why does this happen ?

A

damage to kidney proximal tubule affects 1 alpha hydroyxaltyon of vit D

43
Q

when kidney proximal tubule damaged (falcon syndrome)
–> causes phosphaturia

why does this happen ?

A

damage to kidney proximal tubule affects 1 alpha hydroxylation of vit D

44
Q

dense things like bone = white on XRAY + CT

Muscle + FAT = darker on XRAY + CT

A

-

45
Q

vertebrae - should be paler

- if vertebrae = darker

A

oedema inside bone / sot tissue lesion

46
Q

What is osteoporosis?

A
  • decreased quantity of bone mass
  • -> fragility fractures
  • -> can cause deformity + pain
  • -> with normal microvasculature
47
Q

Note: FRAX risk assessment test

A

-

48
Q

what is osteomalacia?

A
  • decreases bone mineralisation
  • -> forms osteopenic bone
  • -> soft bone
  • if there is too much unmineralized osteoid –> forms looser’s zone.
  • can also form secondary hyperparathyroidism if Ca2+ remains low
49
Q

What are the 3 phases of Paget’s Disease?

A
  • lytic phase
  • mixed lytic/sclerotic phase
  • sclerotic phase
50
Q

What is Paget’s disease?

A
  • disease of bone remodeling
  • -> causes bone pain/deformity/fractures
  • -> patients = prone to osteogenic sarcoma

eLCRS - 머크 (9 decks)

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