Osteomalacia and Rickets
Definition
Osteomalacia: defective mineralisation of existing bone matrix (osteoid) in adults or children.
Rickets: defective mineralisation of newly formed bone at the growth plate in children before growth plate closure.
Aetiology
Aetiology of osteomalacia and rickets is largely the same.
Most common: vitamin D deficiency [Ref]
Rarer causes: [Ref]
- Disorders of vitamin D metabolism (e.g. 1 alpha-hydroxylase deficiency, vitamin D receptor mutation)
- Disorders of phosphate metabolism (e.g. X-linked hypophosphataemia – due to increased FGF23 activity)
Clinical Features
Osteomalacia and rickets have distinctive clinical presentations.
Osteomalacia
Can occur in both adults and children
- Bone pain and tenderness (tend to be diffuse)
- Proximal myopathy
- Difficulty walking
- Waddling gait
- Increased risk of falls
- Severe diseases
- Pathological fractures
- Bone deformity (e.g. bowing of lower limbs)
Rickets
Only occurs in children (before growth plates have fused)
- Impaired growth – not always present
- Short stature
- Delayed walking
- Bone defomirties
- Bowing of the legs
- Genu varum (more common than genu valgum)
- Swelling of the wrists, knees, and ankles (from bone-cartilage junction distension)
- Harrison groove – horizontal depression on the lower edge of the chest (at the attachment point of the diaphragm)
Neonatal presentation: [Ref]
- Late closing of fontanelles and soft skull (craniotabes)
- Poor feeding
- Irritability
- Hypocalcaemic seizures
Investigation and Diagnosis
Blood Tests
Typical biochemical changes (for both osteomalacia and rickets): [Ref1][Ref2]
- ↑ PTH
- ↑ ALP
- ↓ 25-hydroxyvitamin D
- ↓ Calcium ↓ Phosphate (but maybe normal in early disease / mild disease)
Be aware that the test of choice for vitamin D deficiency is serum 25-hydroxyvitamin D, the major circulating form of vitamin D.
Imaging
Typical imaging findings for osteomalacia: [Ref1][Ref2]
- Looser zones (pseudofractures)
- Cortical thinning
- Diffuse osteopaenia (bone appears less dense)
- Pathological fractures possible
Typical imaging findings for rickets: [Ref1][Ref2]
- Growth plate (metaphyseal) abnormalities
- Widening
- Cupping
- Irregularity
- Bone deformities
- Bowing of legs
- Genu varum (more common than genu valgum)
Management
For nutritional deficiency osteomalacia / rickets → ensure adequate vitamin D and calcium [Ref1][Ref2]
- Age-appropriate dose of vitamin D
- Ensure adequate dietary calcium intake
- Give supplementation if insufficient
Notes on various types of vitamin D and their use:
| Vitamin D type | Description | Indication |
|---|---|---|
|
Native forms of vitamin D
|
Must be hydroxylated in the liver to 25-hydroxyvitamin D (calcifediol), then in the kidney into 1,25-dihydroxyvitamin D (calcitriol) for biological activity |
|
| 25-hydroxyvitamin D (calcifediol) | Major circulating form of vitamin D (produced by 25-hydroxylation in the liver)
(If vitamin D deficiency is suspected, 25-hydroxyvitamin D is measured) |
|
Activated vitamin D metabolites (bypassing the renal activation process)
|
Both alfacalcidol / calcitriol can be given as supplements to bypass the renal activation process (thus considered activated vitamin D metabolites):
|
Impaired renal 1-alpha hydroxylase activity:
Not used for routine deficiency replacement or for general population supplementation due to increased risk of hypercalcaemia |