Osteomalacia and Rickets

Question 1

Define Osteomalacia and Rickets

Answer 1

a. Osteomalacia – Softening of bones resulting from impaired mineralization caused by Vitamin D deficiency in adults
b. Rickets – Disturbed bone ossification resulting from impaired minerlaisation caused by Vitamin D deficiency in children

Question 2

How is rickets classified? What is the underlying pathological mechanism in each case?

Answer 2

• Vitamin D deficiency – Dietary lack, increased intake of phytates, increased phosphate intake, decreased exposure to sumlight, malabsorption syndromes
• Decreased 25(OH)2D3 synthesis – Produced in liver. Therefore liver disease or drugs which affect liver metabolism may cause.
• Defective action of 1,25(OH)2D3 - Hormone may be:
  o Abnormal – Vit D administration = curative
  o Absent/defective Vit D receptors – Vit D administration = not curative
• Other – eg. Familial renal tubular defects etc

Question 3

Discuss the pathological events occurring in the bones of children who are vitamin D deficient.

Answer 3

Matrix undergoes defective calcification. This leads to:

1. Hypertrophy of epiphyseal cartilage – Cartilage not being replaced by bone
2. Cessation of diaphyseal calcification – Due to low serum Ca2+
3. Bone resorption in diaphysis – PTH release in attempt to normalize serum Ca2+
4. Bones are stripped of Ca2+ to maintain blood calcium levels
5. Microfractures resulting in deformity

Question 4

Discuss the signs and symptoms of rickets in:

Answer 4

a. Neonates – Generic Ssx
i. Restlessness
ii. Poor sleep
iii. Decreased skull mineralization (craniotabes)

b. Infants – Missed skeletal landmarks
i. Delayed sitting/crawling
ii. Bossing (rounded eminence) of skull bones
iii. Costochondral beading (rachitic rosary)
iv. Delayed fontanelle closure

c. 1-4 age group
i. Enlargement of epiphyseal cartilages at distal ends of the: radius, ulna, tibia, fibula
ii. Kyphoscoliosis
iii. Bow-legedness
iv. Delayed walking

d. >4 years
i. Bow legs
ii. Knock knees

Question 5

List the radiological findings in rickets and osteomalacia

Answer 5

Rickets

• Widened and irregular epiphyseal growth plates – Due to defective calcification
• Widening of metaphyseal region – Due to pressure on weakened bone
• “Cup shaped” metaphysis – Increased load/stress distributed in the centre, less peripherally
• Spotty rarefaction (reduced density) at diaphyseal ends – Due to bone/Ca2+ resorption
• Cortical thinning – Bone/Ca2+ resorption
• Bone deformity - Bowing of long bones and development of knock knees due to excessive load on softened bones
• Looser zones (pseudofractures) – Characteristic finding of rickets and osteomalacia. Narrow transverse radiolucent lines (2-5mm wide) with sclerotic borders that appear bilateral and symmetric that lie perpendicular to the cortical margins

Osteomalacia

• Increased radiolucency – Due to demineralization of bone
• Bone deformity – Bowing of long bones, vertical shortening of vertebrae and flattening of pelvis due to excessive load on softened bones
• Osteopenia (continuous loss of density)
• Looser zones (pseudofractures) – Characteristic finding of rickets and osteomalacia. Narrow transverse radiolucent lines (2-5mm wide) with sclerotic borders that appear bilateral and symmetric that lie perpendicular to the cortical margins

Question 6

Which laboratory investigations are useful in the diagnosis of osteomalacia? Discuss.

Answer 6

Serum
o 25(OH)D3 – extremely low. Synthesised from Vit D in liver
o 1,25(OH)2D3 – extremely low. Synthesised from Vit D in liver
o Phosphate – Low
o Alkaline phosphatase – Increased
o Ca2+ - Low-normal.
o PTH – Increased (attempt to restore normal serum Ca2+)
o Urinary Ca2+ - Decreased. Retained in order to normalize serum Ca2+

Diagnosis
o Hx of inadequate Vit D intake
o X-Rays – Look for radiological findings
o Clinical picture – Look for obvious deformity, Ssx of rickets/osteomalacia
o Dd’s: Hyperparathyroidism, hyperthyroidism, postmenopausal osteoporosis, Cushing’s syndrome