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
  • Crohn's disease, cystic fibrosis
• Impairment in conversion of vitamin D into active metabolites
  • Renal Failure, Liver failure

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

• Hypocalcemia
• Hyperparathyroidism
• Hypophosphatemia
• Malignancy
• Nonaccidental trauma (if evidence of multiple acute or healing fractures)

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)

See Also

• Vitamin D deficiency

References

Authors

Meagan Mackey, Claire, Michael O'Brien, MD, Ross Donaldson, Michael Holtz