Osteomalacia & Rickets

“Normal bone tissue but with abnormal or impaired bone mineralisation resulting in soft bones“

• Rickets: during growth in children
• Osteomalacia: After epiphysis fusion (adults)

Risk Factors

• Poor diet
• Lack of sunlight e.g. northern hemispheres, darker skin (Asian, Afro-Caribbean, Middle Eastern origin), homebound elderly populations
• Prematurity
• Exclusive breastfeeding (especially for > 6 months)
• Medication – phenytoin or other anticonvulsants

Epidemiology

• Common in the past but fortified foods in 20th century have reduced its incidence.
• However, there is a small increase in cases of rickets in UK due to vit D deficiency in a significant number of population
• More common in people with darker skin as they require more sunlight for adequate vitamin D

Aetiology

• Vitamin D, calcium deficiency – most common cause
  • Lack of sunlight
  • Poor dietary intake e.g. low-fat diet, lack of dairy products (vegan diet)
  • Malabsorption e.g. coeliac disease, Crohn’s disease
• Drug-induced e.g. anticonvulsants – use liver and kidney hydroxylase enzymes that convert Vit D for its own metabolism
• Inherited genetic defect – e.g. congenital deficiency of 1 alpha-hydroxylase (promotes the conversion of active Vit D)
• Liver disease e.g. cirrhosis
  • Liver unable to convert inactive vitamin D to 25 hydroxyvitamin D
• Renal failure – kidneys can’t convert 25 hydroxyvitamin D to calcitriol

Clinical Presentation

• Osteomalacia and rickets:
  • Diffuse bone and joint pain
  • Muscle tenderness
  • Proximal myopathy
  • Increased fracture risk with minimal trauma
  • Hypocalcaemia
    • Muscle cramps, twitching, tingling in hands and feet, seizures

• Rickets:
  • Bone pain
  • Soft, weakened bone resulting in skeletal deformities
    • Bowed legs (genu varum)
    • Knock knees
    • Thickening of ankles, wrists and knees
    • Soft skull bones (craniotabes)
    • Delayed closure of fontanelles
    • Prominent frontal bone
    • Scoliosis (rarely)
  • Poor bone growth and development
    • Shorter height than average
  • Protruding abdomen (severe disease)

Pathophysiology

• Calcitriol (vit D3) = hormonally active form of vit D
  • Function:
    • Promote dietary calcium absorption to maintain calcium levels
    • Increases renal tubular calcium reabsorption
    • Increase calcium deposition into bones
    • Promote bone mineralisation, strengthening and formation (after normalisation of Calcium levels)
• Lack of vitamin D → lack of calcitriol → reduced calcium → impaired bone mineralisation (osteoblasts unable to deposit calcium or phosphate into the inorganic matrix)

Investigations

• Blood tests
  • Low 25-hydroxy vitamin D
  • Raised alkaline phosphatase
  • Low calcium and phosphate
  • High PTH
• X-ray
  • Adults – translucent bands, pseudofractures (looser zones) often in superior and inferior pubic rami
  • Children – Metaphyseal cupping and flaring, bowed legs

Management

• Improve dietary intake of Vit D and calcium
• Oral calcium and vit D supplementation or yearly vit D injections
  • Vit D injections mainly necessary if oral intake is not possible or patient has intestinal or liver disease
• Adequate sun exposure
• Treating underlying cause

• Vit D supplementation:
  • Pregnant and breastfeeding women
    • 10mcg of Vit D daily between Oct-March (when days are shorter)
  • Babies from birth to 1 year old (regardless of feeding status)
    • 8.5-10mcg daily supplement
    • Those on formula do not need Vit D as it is fortified unless they are drinking < 500ml a day of formula
  • Children between 1-4 years old
    • 10mcg daily

Complications

• Skeletal Deformities