Diseases

Question 1

Pathophysiology OA

Answer 1

• Decrease water content in ECM (initial increase)
• Decreases no. of GAGs, size of aggrecan, decreased proteoglycan synthesis
• Cytokines IL-1, TNF-a released
• Fillbrilation of cartilage surface
• Loss joint space
• Subchondral sclerosis
• Cysts
• Ostephytes

Question 2

What happens in Vit D deficiency?

Answer 2

• Decreased phosphorous, Ca2+ leading to 2ndary hyperparathyroidism
• Increased PTH leads to increased Ca2+, decreased phosphate reabsorption
• So normal Ca2+, low phosphate

In adults:

• Increased PTH lead to increased bone resorption causing osteopenia
• 2ndary hyperpara leads to decreased phospate reabsorption, normal Ca2+
• Bone matrix can’t be mineralised - osteomalacia (low vit D, Ca2+, phosphate, high PTH)

Question 3

Loss mineralisation bone disorder

Answer 3

Osteomalacia: Low Vit D, Ca2+, phosphate, high PTH
Rickets in children - growth plate doesn’t mineralise, becomes thick and wide - bowing legs
In adults - asymptomatic, bone tenderness, muscle weakenss, looser’s zones/pseudo fractures, osteopenia

Question 4

Increased bone turnover

Answer 4

Paget’s disease:
Increased OB, decreased OC activity causing increase turnover
Bone disorganised, weak, linked to osteosarcoma supressor gene

Hyperparathyroidism
- Increased PTH, increased Ca2+, decreased phosphate

2ndary hyperparathyroidism:
- Hyperdynamic: increased bone turnover

Question 5

Increased bone mass

Answer 5

Osteopetrosis:
Unregulated OB activity, decreased OC activity
Bone dense but weak
Failure bone remodelling, decreased turnover

Question 6

Decreased bone turnover

Answer 6

Renal osteodystrophy:
Increased phosphate
Excess phosphate secreted in gut, binds to Ca2+ leading to decreased Ca2+

2ndary hyperparathyroidism:
Adynamic: decreased OB activity

Question 7

Low bone mass

Answer 7

OP: Increased OC, decreased OB
Normal mineralisation, decreased BMD

Osteogenic imperfecta: defect collagen type I
- Recurrent fractures, ligamentous laxity, decreased muscle tone, bluish sclera

Question 8

Different types of vitamin D dependent rickets

Answer 8

Vit D hydroxlyation deficient rickets type 1a - hydroxylation 1a defect

Vit D hydroxlyation-deficient rickets type 1b - 25 hydroxlyase defiency

Vit D dependent rickets type 2a - defect Vit D receptor gene

Vit D dependent rickets type 2b - defect in hormone response element binding protein - interferes with normal function of receptor