Metabolic bone disease

Question 1

What are the 3 main metabolic bone disorders?

Answer 1

• osteoporosis
• Paget disease
• Rickets and osteomalacia

Question 2

What is osteoporosis?

Answer 2

• condition characterised by weakness of the bones, due to lower than normal bone density
• results in fragility fractures

Question 3

What is a T-score and what are the ranges for osteoporosis, osteopenia, and normal?

Answer 3

• T-score = used to measure bone mineral density (BMD)
• Osteoporosis = T-score < -2.5
• Osteopenia = T-score between -1 and -2.5
• Normal: T-score > -1

Question 4

At what age does peak bone mass occur?

Answer 4

• peak bone mass usually occurs at age 50 and declines thereafter

Question 5

What is the pathology of osteoporosis?

Answer 5

• bone loss is accelerated in osteoporosis by an imbalance between the rates of bone resorption and formation, which are governed by the activity of osteoclasts and osteoblasts respectively

Question 6

What are some risk factors for osteoporosis?

Answer 6

• Non-modifiable: elderly, female, early menopause, small size, family history, steroid use, diabetes
• Modifiable: poor calcium and vitamin D intake, lack of exercise, smoking, alcohol excess

Question 7

How does osteoporosis usually present/first diagnosed?

Answer 7

• patients usually present with fragility fractures and are then screened for osteoporosis

Question 8

What are the 3 typical fragility fractures?

Answer 8

• Colles fracture of the wrist
• Neck of femur fracture
• Vertebral body fracture

Question 9

How do vertebral compression (or wedge) fractures usually present and what is the management?

Answer 9

• usually present with thoracic or lumbar back pain after a minor fall
• often multiple wedge fractures and kyphotic deformity of the spine
• these fractures are stable and treatment is aimed at controlling pain (analgesia)

Question 10

What investigations should be done for suspected osteoporosis?

Answer 10

• DEXA (dual-energy X-ray absorptiometry) scan: to measure BMD
• x-rays: if suspected fractures
• MRI spine: to look for vertebral fractures

Question 11

What is the management for osteoporosis?

Answer 11

• Lifestyle: stop smoking, control diabetes better, diet (vit D, calcium, protein), regular weight-bearing exercise
• Medications: bisphosphonates, denosumab, teriparatide, Adcal-D3, raloxifene, calcitonin
• Prevention of falls: OH, mobility aids etc.

Question 12

What is Paget’s disease?

Answer 12

• a disorder of bone metabolism characterised by focal increases in bone remodelling, resulting in abnormal bone production
• this leads to mechanical weakness of the bone

Question 13

What is the pathology of Paget’s disease?

Answer 13

• increased bone resorption (increased osteoclast activity)
• osteoblasts then respond by producing weak, disorganised bone
• repeated cycles of this result in disorganised bone breakdown and formation

Question 14

What are the clinical features of Paget’s disease?

Answer 14

• often asymptomatic and picked up incidentally on x-ray or raised ALP blood test
• symptoms: bone pain, deformity, fragility fractures

Question 15

What are the investigations for Paget’s disease?

Answer 15

• Bloods: raised ALP, normal Ca, normal phosphate
• X-ray: shows areas of disorganised bone with areas of lysis and sclerosis (the cortex is usually thickened too), pathological fractures
• Isotope bone scans: often show multiple areas of focal increased uptake (sensitive but not specific)

Question 16

What is the management for Paget’s disease?

Answer 16

• analgesia
• bisphosphonates (eg. alendronic acid): inhibits osteoclast activity
• note: monitor at regular 6 or 12 month intervals for recurrence

Question 17

What should be done for patients with Paget’s disease before they go into theatre for surgery if needed?

Answer 17

• Ensure patients are cross-matched for blood in advance of planned surgery
• Pagetic bone is highly vascular and bleeds a lot during surgery

Question 18

Normal vs osteoporotic bone diagram…

Answer 18

Question 19

What is Rickets and what is osteomalacia?

Answer 19

• Both conditions are the result of failure of mineralisation of bone, increased osteoid in osteomalacia
• Rickets: occurs in the growing skeleton
• Osteomalacia (soft bones): occurs in adults

Question 20

What is the main cause of Rickets / osteomalacia?

Answer 20

• vitamin D deficiency

Question 21

What are some causes of vitamin D deficiency?

Answer 21

• poor diet
• low sunlight exposure
• malabsorption

Question 22

What are the clinical features of Rickets and osteomalacia?

Answer 22

• hypocalcaemia symptoms can occur
• Rickets: growth is impaired, older children develop bowing of long bones (varus/valgus deformities of the knee)
• Osteomalacia: tends to present with vague bone pain (localised bone pain may be due to a fracture)

Question 23

What are the investigations for Rickets and osteomalacia?

Answer 23

• Serum alkaline phosphatase (ALP): raised
• Serum vitamin D: low
• PTH: raised
• Calcium and phosphate: low or normal

Question 24

What is the management for Rickets and osteomalacia?

Answer 24

• vitamin D replacement
• (underlying cause of vitamin D deficiency should be addressed)

Question 25

Osteoporosis drug therapies?

Answer 25

• Bisphosphonates: attach to bone crystals and inhibit osteoclast activity, this maintains bone density and reduces risk of fracture
• Adcal D3: calcium is a major mineral found in bone and is important for maintaining healthy bones, vitamin D needed to help body absorb calcium
• Denosumab: monoclonal antibody that targets the RANK ligand
• Teriparatide: form of PTH

Question 26

Why, in Paget’s disease, are both lytic and sclerotic lesions found on plain radiographs of the affected bone?

Answer 26

• Osteoclasts more active, greater bone resorption, you get lytic areas on x-ray
• Osteoblasts lay down bone more randomly, so you get sclerotic areas on x-ray