Rickets

Background
  • Bone disorder characterized by soft, weak, and deformed bones
  • Predominantly caused by Vitamin D deficiency or impaired vitamin D metabolism, but can also be due to hypocalcemia
  • More common in areas with high rates of early childhood malnutrition/starvation
  • The predominant cause is a Vitamin D deficiency, but also inadequate calcium and impaired metabolism of vitamin D may also lead to rickets

Metabolism and Physiology of Vitamin D
  • Gained from diet, supplements, or sunlight exposure
    • Fortified foods (mainstay), supplements, fatty fish, egg yolks, fish liver oil, and some mushrooms
    • Synthesis of vitamin D occurs in the skin through exposure to ultraviolet B radiation from sunlight
  • Hydroxylated in liver→ 25-hydroxyvitamin D, which is further hydroxylated in kidney or extrarenally→ 1,25-dihydroxyvitamin D (active form)
    • Second hydroxylation regulated by PTH, serum calcium, and phosphorus levels
  • Vitamin D acts to:
    • Stimulate intestinal calcium absorption
    • Maintain adequate phosphate levels for bone development
    • Regulate cell growth proliferation and apoptosis
    • Modulate immune function and inflammation reduction

Etiology of Vitamin D Deficiency
  • Inadequate intake
    • Maternal vitamin D deficiency: in utero, 25-hydroxyvitamin D passes through the placenta to the infant
    • Exclusive breastfed infants without vitamin D supplementation
  • Inadequate sunlight exposure, dark skin pigmentation
  • Impaired vitamin D absorption
  • Impairment in conversion of vitamin D into active metabolites

Types of Rickets
  • Hereditary rickets
    • Kidneys unable to retain phosphate
  • Nutritional rickets
  • Vitamin D Resistant Rickets
  • Vitamin D Dependant Rickets
  • Congenital Rickets

Clinical Features
  • Peak incidence between 3 and 18 months of age
  • Bony pain
  • Generalized muscle weakness
  • Hypocalcemia
  • Growth disturbance
  • Enlarged and soft skull (craniotabes), long bones, joints of rib cage ("rickety rosary")
  • Metaphyseal hyperplasia (double malleoli sign, widening of wrist)
  • Bowed legs in toddlers (genu varum), knock-knees in older children (genu valgum)
  • Dental problems

Differential Diagnosis

Evaluation
  • Assess for fractures, if indicated
  • BMP, Mg/Phos, serum calcium

Serum 25-hydroxyvitamin D

Vitamin D assessed by measuring this precursor to hormonally active 1,25-dihydroxyvitamin D

  • Normal range: 75-250 nmol/L
  • Insufficiency: 25-75 nmol/L
  • Deficiency: <25 nmol/L

Management
  • Treat complications (e.g. hypocalcemia, fractures, bone pain)
  • Supplemental vitamin D
    • Initial high-dosage treatment phase: 1,000 IU cholecalciferol per 10 nmol/L required serum increase given daily for 2-3 months
    • Maintenance: 400 IU daily
      • Double dosage for premature infants, infants/children with dark pigmentation, children with limited sun exposure, and obese patients
    • Some populations may require higher dosing (i.e. parathyroid disease, chronic liver disease, renal failure, and malabsorption disorders)

Disposition

See Also

References
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