Metabolic Disorders of Bone

Question 1

What are metabolic bone disorders?

Answer 1

• Abnormalities of bone function

- Abnormalities of bone formation

Question 2

What may be involved in the pathology of metabolic bone disorders?

Answer 2

• Low bone turnover
• High bone turnover
• Loss of mineralisation
• Low bone mass
• High bone mass

Question 3

Give an example of a bone disorder in which low bone turnover plays a part?

Answer 3

• Adynamic disease

- Hypophosphatasia

Question 4

Give an example of a bone disorder in which high bone turnover plays a part?

Answer 4

• Pagets disease
• Hyperparathyroidism
• Thyrotoxicosis

Question 5

Give an example of a bone disorder in which high bone mass plays a part?

Answer 5

-Osteopetrosis

Question 6

Give an example of a bone disorder in which low bone mass plays a part?

Answer 6

• Osteoperosis

- OI

Question 7

Give an example of a bone disorder in which loss of mineralisation plays a part?

Answer 7

• Rickets

- Osteomalcia

Question 8

What biochemical tests can be done to investigate bone?

Answer 8

• Serum Ca/Po4
• Alkaline phosphatase (bone turnover)
• PTH
• Vit D activity
• Specific endocrine test
• Markers of bone turnover
• FGF 23

Question 9

What causes primary hyperparathyroidism and what does this lead to?

Answer 9

• Unregulated PTH secretion leading to hypercalcaemia
• Markedly increases bone turnover
• Bone mass may be retained but in elderly this will often lead to osteoporosis

Question 10

Is PTH always normal as long as it is in the normal range?

Answer 10

NO

Question 11

What is the normal physiological relationship between PTH and Ca?

Answer 11

One goes down the other goes up

See saw relationship

Question 12

What may be seen in an xray of a patient with hyperparathyroidism?

Answer 12

• Brown tumours
• Subperiosteal bone resorption
• Generalised decrease in bone density
• Chondrocalcinosis

Question 13

What happens in fluorosis patients?

Answer 13

They have abnormal matrix mineralisation and fluoride replaces Ca in the matrix.

Question 14

What causes Osteogenesis imperfecta and what does this lead to?

Answer 14

• Genetic disorder
• Various types with various severities
• Caused by defect/deficiency in collagen 1
• Leads to recurrent childhood fractures, deformities, low muscle tone and bluish sclerae in some

Question 15

What happens in patients with space age bone disease?

Answer 15

-Decrease no of osteoblasts due to minimal mechanical stress on bone in zero G environments.

Question 16

What happens in pagets disease and what does this lead to?

Answer 16

• Rapid bone turnover
• Leads to disorganised structure and reduced bone strength
• Increased fracture risk

Question 17

What is pagets disease linked to?

Answer 17

-Osteosarcoma tumour suppressor gene

Question 18

What happens in osteopetrosis and is it genetic or not?

Answer 18

• Failure of osteoclastic activity and chondroclastic resorption
• Failure in remodelling
• Is genetic disorder

Question 19

What happens in osteoporosis?

Answer 19

• Reduced total bone mass as increased osteoclastic activity and decreased osteoblast activity.
• There is however adequte mineralisation of present osteoid
• Collagen function also imparied

Question 20

What is role of estrogen in post menopausal osteoporosis?

Answer 20

• Estrogen deficiency leads to increases bone resorption

- Resorption cavities go deeper and last longer, bone formation also increases but cant keep up.

Question 21

What other subtypes of osteoporosis?

Answer 21

• Post menopausal due to estrogen decrease

- Corticosteroid induced, increases turnover and poor formation and healing