Rickets / Osteomalacia

Snapshot

• A 7-year-old girl is brought to the emergency department after experiencing a risk fracture. The patient fell down to the ground and has not hit her head. This has never happened before. The patient’s parents reports their child states she has pain in bones and at times feels weak. On physical exam, there is tenderness to palpation of the wrist with a waddling gait. Laboratory testing is notable for a decreased serum calcium and phosphate level, and increased alkaline phosphatase and parathyroid hormone. (Rickets secondary to vitamin D defiency)

Introduction

• Clinical definition
  • osteomalacia
    • a condition due to defective mineralization of osteoid
  • rickets
    • a condition due to defective mineralization of cartilage in the epiphyseal growth plates
• Epidemiology
  • demographics
    • children can have both osteomalacia and rickets
    • adults can only have osteomalacia since their growth plates have been fused
  • risk factors
    • vitamin D deficiency secondary to
      • poor dietary intake and sun exposure
      • malabsorption
        • e.g., inflammatory bowel disease and gastrointestinal bypass surgery
      • genetic causes that result in
        • vitamin D deficiency and vitamin D resistance 
    • primary hypophosphatemia
      • e.g., X-linked hypophosphatemic rickets and autosomal dominant hypophosphatemic rickets 
• Etiology
  • vitamin D deficiency  
  • hypophosphatemia
  • chronic kidney disease
    • e.g., metabolic acidosis and decreased 1,25-dihydroxyvitamin D synthesis
  • renal tubular acidosis
    • proximal (type II) renal tubular acidosis/Fanconi syndrome
      • secondary to phosphate wasting, metabolic acidosis which increases calcium loss, and secondary hyperparathyroidism
  • inhibitors of bone mineralization
    • e.g., bisphosphonates, alimunum, and fluoride
  • hypophosphatasia
    • a tissue non-specific alkaline phosphatase (TNSALP) gene mutation that leads to the accumulation of pyrophosphate
      • pyrophosphate inhibits bone mineralization
• Pathogenesis
  • impaired mineralization of osteoid (osteomalacia) and/or cartilage at the epiphyseal plates (rickets)
• Prognosis
• depends on the etiology

Presentation

• Symptoms
  • bone and joint pain
  • muscle weakness
  • difficulty with walking
  • fractures
• Physical exam
  • pediatric 
    • bowed legs
    • rachitic rosary line
      • costochondral thickenings 
    • Harrison’s groove
      • depression along line of diaphragmatic insertion into rib cage
    • kyphosis 
      • as well as lordosis and scoliosis 
    • poor growth
• bone tenderness to palpation

Imaging

• Radiography
  • indication
    • perform in patients with a clinical presentation concerning for osteomalacia or rickets
  • findings
    • radiolucency (decreased bone density)
    • physeal widening
    • metaphyseal cupping
    • prominence of rib heads at the osteochondral junction (rachitic rosary)
• bowing (often genu varum)

Studies

• Labs
  • highly dependent on the cause
    • e.g., patients with vitamin D deficiency will have decreased 25-hydroxyvitamin D

Laboratory Abnormalities in Select Bone Disorders
Etiology	Serum Phosphate	Serum Calcium	Serum Alkaline Phosphatase	Parathyroid Hormone
Osteomalacia/rickets	Decreased	Decreased	Increased	Increased
Osteoporosis	Normal	Normal	Normal	Normal
Osteopetrosis	Normal	Normal or decreased	Normal	Normal
Paget disease of the bone	Normal	Normal	Elevated	Normal
Osteitis fibrosa cystica	Primary hyperparathyroidismdecreasedSecondary hyperparathyroidismincreased	Primary hyperparathyroidismincreasedSecondary hyperparathyroidismdecreased	Primary and secondary hyperparathyroidismincreased	Primary and secondary hyperparathyroidismincreased
Hypervitaminosis D	Increased	Increased	Normal	Decreased

Differential

• Child abuse
• Osteogenesis imperfecta
• Osteoporosis
• Paget disease of bone
• Multiple myeloma

Treatment

• Medical
  • treatment is directed against the underlying cause for example
    • vitamin D supplemention
      • indication in patients with
        • vitamin D deficiency
        • hereditary hypophosphatemic rickets along with phosphate supplementation
• osteomalacia of renal tubular acidosis along with sodium or potassium citrate

Complications

• Fractures
• Growth abnormalities