Osteomalacia and Rickets

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Basics

Description

  • A metabolic bone disorder due to decreased bone mineralization (calcification) and increased organic bone matrix that results in decreased bone density
  • Referred to as renal osteodystrophy when secondary to renal disease
  • System(s) affected: musculoskeletal

Epidemiology

  • Children
    • Median age of presentation is 15 months.
    • Infants develop vitamin D–deficiency rickets (1).
    • Adolescents develop nutritional rickets due to calcium deficiency (1).
  • Adults: elderly, rare and increasing

Incidence
In the United States, occurs almost exclusively in breastfed infants without vitamin D supplementation or sun exposure

Etiology and Pathophysiology

  • Abnormalities of mineralization ossification or interference caused by insufficient circulating levels of calcium, phosphate, or vitamin D
  • Children: Rickets is a disease of the physes (growth plates) characterized not only by deficient mineralization of cartilage and osteoid but also by retarded endochondral ossification, which causes excessive accumulation of physeal cartilage, growth failure, and skeletal deformities.
  • Adults: disorder of mineralization of newly formed bone matrix
  • Impaired intestinal absorption of calcium/phosphorus due to celiac disease, cystic fibrosis, or postgastrectomy
  • Hypophosphatemia from secondary hyperparathyroidism due to vitamin D deficiency is the primary cause in adults.
  • Vitamin D–metabolism abnormalities, including hepatic or renal disease
  • Resistance to vitamin D
  • Impaired renal phosphate absorption associated with proximal or distal renal tubular defects
  • Causes that inhibit mineralization of the growth plate and osteoid
    • Alkaline phosphatase deficiency
    • Aluminum toxicity
    • Fluoride toxicity
    • Primary hyperparathyroidism
  • Drugs that may affect absorption or metabolism of calcium, phosphorus, or vitamin D
    • Antacids
    • Antiepileptic drugs
    • Corticosteroids
    • Loop diuretics
  • Drugs that inhibit mineralization: bisphosphonates
  • Oncogenic osteomalacia
  • Sickle cell

Genetics

Heritable disorders of rickets include (2):

  • Vitamin D–dependent rickets type 1—causes reduced or no renal synthesis of 1,25-dihydroxyvitamin D (calcitriol)
  • Vitamin D–dependent rickets type 2—causes partial or complex resistance to calcitriol, resulting in elevated levels of calcitriol
  • Vitamin D–dependent rickets type 3—prevents the action of calcitriol in transcription causing resistance and elevated levels calcitriol
  • Autosomal dominant hypophosphatemic rickets—causes phosphaturia, decreased intestinal absorption of phosphorus, and decreased 25-hydroxyvitamin D (calcidiol), resulting in low calcitriol
  • X-linked hypophosphatemic rickets—causes phosphaturia, decreased intestinal absorption of phosphorus, decreased calcidiol, resulting in low calcitriol

Risk Factors

  • Eating disorder
  • Increased melanin skin pigmentation
  • Malabsorption
  • Vegetarian diet without vitamin supplementation
  • Limited sunlight exposure (high latitude, overcrowding, religious customs limiting adequate skin exposure to UV irradiation, working indoors)
  • Poverty
  • Children
    • Breastfeeding as a sole source of nutrition without vitamin D supplementation
    • Breastfed infants born to mothers who themselves are vitamin D deficient
    • Prematurity
  • Adults
    • Poor diet low in calcium and high in phytate
    • Primary biliary cirrhosis
    • Renal failure
    • Gastrectomy

General Prevention

  • Adequate vitamin D intake: Encourage foods, such as fatty fish, cod liver oil, egg yolks, and fortified foods (3)[C].
  • Children
    • American Academy of Pediatrics recommends a minimum vitamin D intake of 400 IU/day starting within the first few days of life.
    • Infants who consume >1 L/day of vitamin D–fortified formula or whole milk will receive the recommended vitamin D intake.
    • Supplementation is recommended for breastfed infants and children consuming <1 L/day of vitamin D–fortified formula or milk.
  • Adults
    • ≤70 years old, vitamin D, 600 IU/day (4)[A]
    • ≥71 years old, vitamin D, 800 IU/day (4)[A]
  • Adequate calcium intake:
    • ≥4 years old, calcium, >1,000 mg/day (4)[A]
    • If calcium-rich foods are unavailable, then powdered limestone, calcium-rich vegetables, and/or ground bony fish powder (1)[C]
  • Pregnancy (4)[A]
    • Ergocalciferol 600 IU/day for routine pregnancy
    • Ergocalciferol 1,000 to 2,000 IU/day is safe if vitamin D–deficient.

Commonly Associated Conditions

  • Children with vitamin D–deficiency rickets
    • Secondary hyperparathyroidism
    • Dilated cardiomyopathy
    • Marrow fibrosis with pancytopenia or microcytic hypochromic anemia
    • Dysregulation of immune function and cellular differentiation and proliferation
  • Adults with osteomalacia
    • Chronic renal disease
    • Gastrectomy
    • Epilepsy
    • Malnutrition

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