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For further information, see CMDT Part 26-19: Rickets & Osteomalacia

Key Features

Essentials of Diagnosis

  • Low bone density from defective mineralization

  • Caused by deficiency in calcium, phosphorus, or low alkaline phosphatase

  • Rickets: defective bone mineralization in childhood or adolescence before epiphyseal fusion

  • Osteomalacia: defective bone mineralization in adults with fused epiphyses

  • Painful proximal muscle weakness (especially pelvic girdle); bone pain

  • Low serum 25-hydroxy-vitamin D (25-OHD), hypocalcemia, hypocalciuria, hypophosphatemia, secondary hyperparathyroidism

  • Classic radiologic features may be present

General Considerations

  • Rickets: Defective mineralization of growing skeleton in children

  • Osteomalacia: Defective skeletal mineralization in adults

  • Causes of osteomalacia (Table 26–10)

    • Vitamin D deficiency

      • Most common cause

      • ~25% of postmenopausal women have some vitamin D deficiency

      • 60% of the institutionalized elderly not receiving vitamin D supplementation

      • Incidence varies among regions: < 1% in Southeast Asia, 29% in the United States

      • Incidence of severe vitamin D deficiency (serum 25[OH]D < 20 nmol/L [50 nmol/L]) is 3.5% in the United States

      • May arise from insufficient sun exposure, malnutrition, malabsorption, nephrotic syndrome

      • Cholestyramine, orlistat, and anticonvulsants decrease vitamin D levels

    • Dietary calcium deficiency, eg, in malnourished, elderly patients

      • Milk, especially skim milk, is a poor source of vitamin D

    • Phosphate deficiency, eg, due to

      • Nutritional deficiency

      • Alcoholism

      • Phosphate-binding antacids (eg, aluminum hydroxide)

      • Genetic disorders (vitamin D–resistant rickets)

      • Renal tubular acidosis

      • Fanconi syndrome

    • Aluminum toxicity due to chronic hemodialysis with tap water dialysate or from aluminum-containing phosphate binders

    • Oncogenic osteomalacia

      • Caused by excessive production of phosphatonin by soft tissue tumors

      • Hypophosphatemia, excessive phosphaturia, reduced serum 1,25(OH)2 D3 concentrations, osteomalacia

    • Disorders of bone matrix, eg, hypophosphatasia (deficient alkaline phosphatase)

    • Fibrogenesis imperfecta

Table 26–10.Causes of osteomalacia.1
Table 26–9.Causes of osteoporosis.1

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