8.4 Bone Loss Conditions

Question 1

Describe the microscopic appearance of a spongy bone trabecule

Answer 1

• Osteoclasts present
• Osteocytes sitting in lacunae, connected to canaliculi
• Lamellae (not concentric, though) sit in fibre. Strength of trabecule is proportional to square of diameter; more lamellae = more strength.

Question 2

Describe the microscopic appearance of cortical bone

Answer 2

• Blood vessels and nerves in haversian canal
• Surrounding by concentric lamellae
• Osteocytes in lacunae, connected by canaliculi

Question 3

Compare the microscopic appearance of normal vs osteoporotic bone

Answer 3

Osteoporotic bone has much thinner trabeculae, and sometimes broken.

Question 4

List as many risk factors for hip fractures as you can think of

Answer 4

• Corticosteroids
• Low BMI
• Old age
• Anticonvulsants (and seizures)
• Rheumatoid arthritis
• Low BMD
• Smoking

Question 5

What is the link between coeliac disease and osteoporosis?

Answer 5

• Decreased area of gut
• Decreased ability to absorb calcium
• Therefore, decreased ability to regrow new bone
• Osteoporosis

Question 6

What is the link between inflammatory bowel disease and osteoporosis?

Answer 6

• Decreased ability to absorb calcium
• Medications such as corticosteroids increase risk
• Inflammatory cytokines reduce bone density

Question 7

How do kidney and liver disease cause osteoporosis?

Answer 7

Inability to convert vitamin D3 into calcidiol (liver) and calicitriol (kidney), leading to decreased calcium uptake.

(Kidney disease can also cause secondary hypoparathyroidism)

Question 8

How does multiple myeloma cause osteoporosis? (and other cancers)

Answer 8

• Myeloma cells produce osteoclast-activating cytokines
• Increased bone breakdown

Question 9

Why does hyperthyroidism cause osteoporosis?

Answer 9

Increased thyroxine can increase bone turnover.

Question 10

Why does rheumatoid arthritis cause osteoporosis?

Answer 10

Increased inflammatory cytokines, decreased bone mass.

Question 11

Explain why glucocorticoids (like cortisol) are so bad for your bone, using the 4 main aspects of damage

Answer 11

1. Decreased GI Ca2+ absorption (inc. PTH)
2. Decreased renal reabsorption of Ca2+
3. Decreased sex steroid secretion
4. Decreased osteoblast activity

Question 12

What happens to mineral/non-mineral proportions in bone in osteoporosis, osteopaenia, and osteomalacia relative to normal?

Answer 12

Osteopaenia/porosis: same proportion, lower overall volume (-porosis moreso)

Osteomalacia: lower mineral content, normal non-mineral (hence Malakos = soft)

Question 13

How does Paget’s disease differ from osteoporosis?

Answer 13

• LOCALISED increase in bone turnover
• Also, disorganised collagen

Question 14

Which micronutrients are important in bone loss disease?

Answer 14

• Vitamin D
• Calcium
• Phosphate

Question 15

What T score is required for osteoporosis?

Answer 15

-2.5 or less

Question 16

What is the diagnostic definition of a vertebral deformity (in terms of compression fracture)?

Answer 16

20% or more decrease in height

Question 17

Why do we do a TSH test in osteoporosis workup?

Answer 17

Hypo can increase fall risk.

Hyper can cause increased bone loss.

Question 18

How long does it take, roughly, for osteoblasts to produce a new bone matrix during bone remodelling?

Answer 18

3 months

Question 19

Describe 3 aspects of non pharmacological management of osteoporosis

Answer 19

1. Diet: get enough calcium
2. Sun: get enough Vit D (very hard to get in food)
3. Exercise: weight-bearing exercises

Question 20

List two antiresorptive drugs, and outline their mechanisms

Answer 20

Bisphosphonate: Taken up by osteoclasts, and impair action/increase apoptosis

Denosumab: monoclonal antibody that binds to RANKL, preventing osteoclast formation.

Question 21

What are some side effects of bisphosphonates? What else should we tell patients when prescribing them?

Answer 21

• Upper GI (e.g. heartburn)
• Acute phase (systemic inflammatory rxn)

Should be taken with water. Wait at least 30mins before eating after.

Question 22

Why should we be careful when deprescribing denosumab?

Answer 22

Bone density falls quicker after stopping than would be expected with bisphosphinates.

Question 23

Romosozumab is an antibody to which protein? What are the two effects of this? What must be considered when ceasing?

Answer 23

• Sclerostin antibody
• Decreases resorption, increases formation
• Must prescribe antiresorptive upon cessation