Osteomalacia & Rickets profoma Flashcards
What is osteomalacia & rickets?
FAILURE OF MINERALISATION OF BONE due to Vitamin D deficiency.
Osteomalacia - characterised by incomplete mineralisation of the bone matrix (osteoid) following growth plate closure in adults.
Rickets - characterised by defective mineralisation of the epiphyseal growth plate cartilage in children.
Epidemiology of osteomalacia & rickets
US, Europe and East Asia, more than 40% of adult population older than 50 yrs are vitamin D deficient
In developing countries, vitamin D deficiency leading to rickets is reported in 60% of infants.
In Middle East, high prevalence of osteomalacia is reported in Muslim women- due to increased clothing coverage of the skin.
Foods w/ vitamin D &supplements have reduced the incidence of osteomalacia.
Aetiology of osteomalacia & rickets. What are the causes of vitamin D Deficiency?
- Vitamin D deficiency - most common.
Causes of vitamin D deficiency
- Low dietary intake
- Inadequate UV-B sunlight exposure e.g. homebound elderly populations or those that cover up for religious reasons.
- Intestinal malabsorption e.g. coeliac disease, gastric surgery or Crohn’s disease.
- Drugs- can affect vitamin D metabolism e.g. anticonvulsants such as Phenytoin.
- Liver disease
- Renal disease
- Hypophosphataemia - ↓ phosphate, PO₄³⁻ - much rarer cause.
- Rare hereditary causes
Pathophysiology of osteomalacia/rickets - What causes the defective bone mineratisation? What does adequate bone mineralisation rely on? Explain why phosphate is important for bone mineralisation.
Osteomalacia results from defective bone mineralisation - because osteoblasts do not have enough Ca or phosphate to solidify the osteoid (made of type 1 collagen).
This is a result of a lack of 1 or more factors needed for osteogenesis:
- Lack of Ca
- Lack of Phosphate → induces ↓ Ca + ↓es efficacy of 1-⍺-hyroxylase →↓es 1,25(OH)2D →↓es gut’s ability to absorb Ca.
- Abnormal pH at the site of calcification
Mineralisation depends on factors that supply adequate Ca & PO₄³⁻ to bones:
- Vitamin D maintains Ca & PO₄³⁻ homeostasis - through its actions on the GI tract, the kidneys, bone & parathyroid glands.
Pathophysiology of osteomalacia/rickets - Explain Vitamin D hydroxylation & how it is linked to osteomalacia.
- There are 2 inactive forms of vitamin D that exist:
- Vitamin D2 (ergocalciferol) - plant derived & consumed in food
- Vitamin D3 (cholecalciferol) - formed from the effect of UV-B sunlight on 7-dehydrocholesterol in skin. - Both forms bind to vitamin D binding protein in blood
- Vitamin D2 & D3 are hydroxylated to 25-hydroxyvitamin D in liver (25(OH)D).
- Requires enzyme 25-hydroxylase - 25-hydroxyvitamin D is then hydroxylated in kidney to form active vitamin D form, 1,25-dihydroxyvitamin D (1,25(OH)2D)
- requires 1-⍺-hydroxylase
Pathophysiology of osteomalacia/ rickets- What are the functions of 1,25-dihydroxyvitamin D?
- Maintains normal Ca absorption in intestines.
Inadequate absorbtion of Ca → low serum Ca → secondary hyperparathyroidism (PTH is trying to ↑ Ca levels) → PTH stimulates osteoclasts & bone resorption → osteopenia.
- Supresses gene transcription for PTH. So it promotes bone mineralisation. Less 1,25-vitamin D = more PTH = more bone resorbtion.
Risk factors for osteomalacia/ rickets
- Dark skinned individuals
- Breast fed babies
- Elderly & infirm
- Neoneates
- Malabsorption diseases e.g. Crohn’s, Coeliacs, bariatric procedures.
- Chronic liver disease
- Chronic renal failure
- Strict diets e.g. lacto vegetarian
- Excessive high factor sun block
Clinical features of osteomalacia
- Bone & joint pain - especially long bones & pelvic area
- Proximal muscle weakness - may lead to waddling gait or struggle to walk upstairs.
- Osteopenia
- Fractures - especially neck of femur- due to bone fragility
- Malaise & fatigue
- Muscle spasms & numbness
- Skeletal deformity
- Lethargy, tetany & convulsions - due to hypocalcaemia can occur.
Clinical features of rickets
They have all the general symptoms of osteomalacia too.
Common in children under 12 months:
- Craniotabes- softening of skull bones - prominent frontal bone.
- Rachitic rosary - a row of bead like prominences at the junction of a rib & its cartilage, resembling a rosary.
- Protruding abdomen
Common in older children:
- Genu varum - bow legs
Investigation for osteomalacia & rickets: lab abnormalities
- Low serum vitamin D - undetectable.
- Low calcium - can be normal unless the disease is advanced.
- Low phosphate - can be normal.
- Raised serum alkaline phosphatase
- Raised PTH levels
- Low urinary calcium excretion - tests serum urea and creatinine.
Investigations for osteomalacia/ rickets: X-rays in osteomalacia
Looser’s zones fractures
- Translucent bands (also called pseudo fractures).
- Looser’s zones are common in the ribs, pelvis, neck of femur and long bones.
NOTE- view x-ray on notes!
Osteopenia
Bone bending
Hour glass thorax
Investigations for osteomalacia/ rickets: X-rays in rickets
Thickening & widening of epiphyseal (growth) plate (fraying)
Metaphyseal cupping & flaring
Metaphyseal fraying- fuzzing & irregular
Delayed opacification of the epiphyses
Thin cortices
Delayed closure of the skull bones (fontanelles)
Bowing of legs
NOTE: view x -ray on notes!
Management for osteomalacia/ rickets
Vitamin D3 supplementation e.g. 10,000 to 25,000 IU for 2-4 weeks = elevates serum 25(OH)D & reduces PTH.
- Dose can then be reduced to maintenance dose btw 800 to 1600 IU (except in patients w/ malabsorption).
- In infants & young children, vitamin D drops used.
- Intramuscular used in malabsorption patients.
NOTE: vitamin D injections in the elderly is linked to increased FALLS
Ensure adequate dietary CALCIUM w/ vitamin D
Preventive measures:
- take vitamin D supplements during pregnancy, for infants & children
Prognosis for osteomalacia/rickets
Most people w/ osteomalacia will recover w/ treatment
However, can take months for bones to recover & for muscles to become strong again.
Late diagnosis can make recovery more difficult, especially if bones have fractured.
