Osteomalacia: qualitative defect of bone with abnormal softening of the bone due to deficient mineralization of osteoid (immature bone) secondary to inadequate amounts of calcium and phosphorus

Rickets: the same disease occurring in children which has subsequent effects on the growing skeleton

Aetiology

• The principal causes of osteomalacia and rickets involve either insufficient calcium absorption, or phosphate deficiency caused by increased renal losses
• Vitamin D deficiency - malnutrition/malabsorption, lack of sunlight exposure
• Hypophosphateamia
  • Re‐feeding syndrome
  • Alcohol abuse - impairs phosphate absorption
  • Malabsorption
  • Renal tubular acidosis
• Long term anticonvulsant use
• Chronic kidney disease - reduced phosphate resorption and failure of activation vitamin D, resulting in secondary hyperparathyroidism
  • Some renal diseases are inherited disorders (X‐linked hypophosphataemia or vitamin D resistant rickets)

Pathophysiology

Vitamin D deficiency

• Vitamin D stimulates absorption of calcium from GI tract, kidney and bone, also induces osteoblasts to release osteocalcin
• Vitamin D deficiency leads to hypocalcaemia and elevated PTH
• This increases calcium absorption, osteoclastic activity, and release of Ca2+ from bone
• Results in impaired mineralisation of newly formed osteoid (thick osteoid seams)
• Bone is weakened - prone to fracture (micro-fractures or gross fractures)

Clinical features

Symptoms

• Bone pain - pelvis, spine and femora
• Symptoms of hypocalcaemia - paraesthesiae, muscle cramps, irritability, fatigue, seizures, brittle nails
• Sustain pathological fractures easily