Osteomalacia & Rickets

General Information

Classification: Skeletal
Figure 1 Classic presentation of Rickets (due to vitamin D deficiency) with lower extremities bowing outward (Source: OpenI, NLM)

What is it?

“Soft bones” due to inadequate bone mineralization, primarily in adults

Rickets:

  • Analogous to osteomalacia in children
  • More severe bone deformities/pain since bone growth is still present (occurs before epiphyseal plates close)

Risk Factors: deficiencies in vitamin D/calcium/phosphates (cold weather/less sun exposure, darker skin, obesity), maladaptive absorption of aforementioned metabolites (Crohn disease, celiac disease), kidney/liver disease, hypocalcemia, anti-epileptics, antifungals

Evaluation

Signs & Symptoms

  • Pain when weight is applied on weakened bones (especially pelvis, ribs, hips)
  • Waddling gait
  • Fractures/pseudofractures, spinal/lower extremity deformities
  • Positive Chvostek/Trousseau sign
  • Rickets:
    • Bowing of legs (Figure 1): genu varum
    • Rachitic rosary
    • Widened epiphyseal plates

Lab

  • Elevated PTH, alkaline phosphatase
  • Low Ca2+

Pathophysiology

Physiological Blurb: Vitamin D Synthesis

Endogenous vitamin D (VitD): from UVB

  1. UVB rays stimulate conversion of 7-dehydrocholesterol into cholecalciferol/D3 in the stratum spinosum/basale
  2. In the liver, this is then converted to 25-hydroxycholcalciferol via VitD-25-hydroxylase
  3. Then transported to the kidneys, where can finally synthesize active form of VitD calcitriol/1,25-dihydroxycholecalciferol via 1-alpha-hydroxylase)

Exogenous VitD: fish olive oil, egg yolk, fortified in dairy products

Chronic kidney/liver disease or injury leads to higher rates of deficiency of VitD (since many of the processes occur in these organs)

  • Lower concentrations of VitD lead to decreased Ca2+ absorption in the SI, increased PTH (increased bone turnover, decreased matrix deposition)
  • Osteocytes secrete fibroblast GF 23, inhibiting resorption of phosphate in kidneys, leading to decreased bone mineralization

Treatment

Addressing VitD deficiency (Gold standard)

VitD supplements: Ergocalciferol (Vit D2) or cholecalciferol (D3; preferred)* orally

Calcium supplements: calcium carbonate/citrate

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