Osteomalacia

Question 1

What is the epidemiology of osteomalacia?

Answer 1

Common in the elderly and dark skinned populations, or those that cover their skin for religious reasons

Premature babies

Question 2

What is the aetiology of osteomalacia?

Answer 2

Vitamin D deficiency:

• Due to lack of sunlight and/or dietary intake; including infants younger than 1yr (as breast milk is low in Vit D)
• Low intestinal absorption e.g. CF, coeliac, chronic pancreatitis

Defects in vit D metabolism: - Liver cirrhosis

• CYP450 inducers (increase the metabolism of vit D) e.g. anticonvulsants
• Renal disease (CKD)

Inherited forms:
- Type 1 hereditary vitamin D dependent rickets - ineffective conversion of vit D precursors in the
kidney to active vit D; autosomal recessive
- Type 2 hereditary vitamin D dependent rickets – mutations in the 1,25(OH)D receptors → end organ
resistance to vit D

Vit D independent forms: (Rare)

• Renal tubular acidosis
• Ca and/or phos deficiency
• Hypoparathyroidism
• Bisphosphonates, aluminium, fluoride

Question 3

What is the pathophysiology of osteomalacia? And rickets?

Answer 3

Osteomalacia:
- Normal bone formation (adequate bone matrix/osteoid/type 1 collagen formed by osteoblasts) with abnormal mineralisation

Rickets:
- Same processes but in paediatrics - impaired mineralisation of cartilaginous growth plates (can occur alongside osteomalacia in paeds)

Question 4

How does osteomalacia present? And rickets?

Answer 4

Osteomalacia:

• In adults AND children
• Bone pain + tenderness
• Pathological fracture
• Waddling gait + difficulty walking
• Symptoms of hypocalcaemia
• Myopathy (weakness, spasm cramps)
• Bone deformity in severe cases

Rickets:

• ONLY children
• Bone deformity: bending of long bones; distension of bone-cartilage junctions e.g. rachitis rosary = bead-like distension of bone-cartilage junction of ribs; craniotabes = softening of skull; genu varum = bow legs
• Late closing of fontanelles
• Impaired growth
• Hypocalcaemia

Question 5

What are the blood results in osteomalacia/rickets?

Answer 5

Calcium - low
Phosphate - low
Alk phos - high
PTH - high

Question 6

What are the X-ray findings in osteomalacia? And rickets?

Answer 6

Both:

• Low bone mineral density
• Thin cortices

Osteomalacia:
- Looser zones/pseudofractures = transverse bands of radiolucency indicating defectivev calcification of osteoid

Rickets:

• Growth plates in the metaphysis of long bones = less defined + presence of cupping, siplling and fraying
• Wide epiphysis
• Evidence of bone deformities (of skull, femur etc)

Question 7

How do yo treat osteomalacia and rickets?

Answer 7

If vit D deficient - 25[OH]D levels <25nmol/L (or 25-50 + symptomatic or other risks:

• Give Vit D - can give high doses safely (up to 300,000 IU) to return plasma levels to normal
• Supplement vit D and Ca long term
• Also indicated in exclusively breastfed infants

Otherwise, treatment of the underlying cause (removal of medications, malabsorption condition etc)