Osteomalacia

Question 1

Describe osteomalacia?

Answer 1

• Normal amount of bone but mineral content is low
  
  • Excess uncalcified osteoid and cartilage
• Rickets if this occurs during bone growth
• Osteomalacia if this occurs after epiphyses fusion

Question 2

Signs and symptoms of Rickets?

Answer 2

• Growth retardation, hypotonia, apathy
• Knock-kneed, bow-legged
• Features of low calcium

Question 3

Signs and symptoms of Osteomalacia?

Answer 3

• Bone pain and tenderness
• Fractures (esp femoral neck)
• Proximal myopathy due to reduced PO₄^3- and vitamin D

Question 4

Causes of osteomalacia?

Answer 4

• Vitamin D deficiency / resistance
• Liver disease
• Drug-induced
• Tumour-induced
• Renal osteodystrophy

Question 5

Causes of vit D deficiency?

Causes of vit D resistance?

Answer 5

• Deficiency: malabsorption, poor diet, lack of sunlight
• Resistance: inherited

Question 6

Causes of drug-induced osteomalacia?

Answer 6

• Anticonvulsants
  
  • Induce liver enzymes
  • => Increased breakdown of 25-hydroxy-vitamin-D

Question 7

Describe the investigations into osteomalacia?

Answer 7

• Plasma
  
  • Reduced Ca, PO₄^3-, 25(OH)-vitamin D
  • Raised ALP, PTH
• Biopsy
  
  • Bone => Incomplete mineralization
  • Muscle => Normal
• X-ray
  
  • Loss of cortical bone
  • Cupped, ragged metaphyseal surfaces in rickets

Question 8

Describe the treatment for osteomalacia?

Answer 8

• Dietary insufficiency: vitamin D (calcium D₃ PO)
• Malabsorption: vitamin D (ergocalciferol PO)
• Renal disease/vit D resitant: alfacalcifdol
• *Plasma Ca²⁺ monitoring

Question 9

SEs of alfacalcidol?

Answer 9

Hypercalcaemia

Question 10

Describe vitamin D-resistant rickets?

Answer 10

• Type 1
  
  • Low renal 1a-hydroxylase activity
• Type 2
  
  • End-organ resistance to 1,25-dihydroxy-vitamin D₃
  • Due to point mutation in receptor
• Tx for both: High dose calcitriol

Question 11

Describe X-linked hypophophataemic rickets?

Answer 11

• Defect in renal phosphate handling
  
  • Mutations in PEX or PHEX genes
• Plasma phosphate low (phosphaturia), ALP high
• Tx: high dose oral phosphate and calcitriol