Osteomalacia and Rickets

Rickets vs Osteomalacia - Bone Basics Banter

• Shared Pathophysiology: Deficient mineralization of osteoid; commonly from Vitamin D deficiency, leading to soft, weak bones.
• Shared Biochemistry: Typical: ↓ Serum $Ca^{2+}$ & $PO_4^{3-}$; ↑ PTH (secondary hyperparathyroidism), ↑ Alkaline Phosphatase (ALP).

Etiopathogenesis - Vitamin D Void

• Core Problem: Insufficient active Vitamin D ($1,25(OH)_2D$) or its action.
  • Deficiency Sources:
    • ↓ Sunlight (UVB) exposure: Key for skin synthesis.
    • ↓ Dietary intake: Fortified foods, oily fish.
    • Malabsorption: Celiac, Crohn's, cholestasis.
  • Impaired Metabolism/Action:
    • Liver disease: ↓ $25$-hydroxylation to $25(OH)D$.
    • CKD: ↓ $1\alpha$-hydroxylase activity, ↓ $1,25(OH)_2D$.
    • Drugs: Anticonvulsants (phenytoin) accelerate Vitamin D catabolism.
    • Hereditary Vitamin D Resistant Rickets (HVDRR): End-organ resistance due to VDR gene mutations.
• Simplified Pathophysiology:

> ⭐ In Vitamin D deficiency, hypophosphatemia is often more pronounced than hypocalcemia due to PTH's effect on renal phosphate excretion and calcium mobilization.

Clinical Manifestations - Skeletal Signs

📌 Rickets Deformities Mnemonic: "BROWS"

• Bowing of legs (genu varum/valgum)
• Rachitic rosary (costochondral beading)
• Outstanding frontal bossing
• Widened epiphyses (e.g., wrists)
• Sulcus (Harrison's)

⭐ Looser's zones (pseudofractures) are hallmark stress fractures in osteomalacia, often bilateral and symmetrical, typically seen in scapulae, ribs, pubic rami, and femoral necks.

Diagnostic Workup - Lab & X‑Ray Clues

• Biochemical Markers: Impaired mineralization & secondary HPT.

  Marker	Osteomalacia/Rickets
  Serum Ca	↓ or Normal
  Serum P	↓ (Markedly)
  ALP	↑↑ (Significantly)
  PTH	↑ (Secondary HPT)
  25(OH) Vit D	↓ (Deficiency <20 ng/mL; Insufficiency 20-29 ng/mL)

• Radiological Signs:

  • Osteomalacia:
    • Looser's zones (pseudofractures): Hallmark; incomplete transverse radiolucencies. Sites: femoral neck, pelvis, scapula.
  • Rickets (in growing bones):
    • Metaphyses: Cupping, fraying, splaying.
    • Widened physis (epiphyseal plate).
    • Rachitic rosary (costochondral).
    • Long bone bowing.

⭐ Looser's zones (Milkman's fractures), pathognomonic for osteomalacia, are often bilateral, symmetrical stress fractures through demineralized bone cortex.

Treatment Strategies - Bone Boosters

• Vitamin D (Cholecalciferol - D3):
  • Daily Therapy (6-12 weeks):
    • Infants (<1yr): 2000 IU/day.
    • Children (1-18yr): 2000-5000 IU/day.
    • Adults: 6000 IU/day or 50,000 IU/week.
  • Stoss Therapy (Single dose): 100,000-600,000 IU oral/IM (age-dependent).
• Calcium Supplementation:
  • Elemental Calcium: 500-1000 mg/day (Children: 30-75 mg/kg/day).
• Address Underlying Conditions: e.g., GI, renal, liver disease.
• Surgical Correction: For residual deformities post-biochemical correction.

⭐ Stoss therapy (Vitamin D 300,000-600,000 IU for older children/adults) ensures rapid repletion and adherence.

High‑Yield Points - ⚡ Biggest Takeaways

• Rickets occurs in children (growing bones), Osteomalacia in adults (mature bones); both due to defective mineralization of osteoid.
• Most common cause: Vitamin D deficiency leading to impaired calcium and phosphate absorption.
• Key feature: Accumulation of unmineralized osteoid.
• Rickets: Bowing deformities (genu varum/valgum), rachitic rosary, widened epiphyses, craniotabes.
• Osteomalacia: Diffuse bone pain and tenderness, muscle weakness, pathological fractures, Looser's zones (pseudofractures).
• Labs: ↓ Serum Ca²⁺, ↓ Serum PO₄³⁻ (or normal), ↑ Alkaline Phosphatase (ALP), ↑ Parathyroid Hormone (PTH), ↓ 25-hydroxyvitamin D.
• Radiographic signs: Osteopenia, cortical thinning; cupping, fraying, splaying of metaphyses in rickets.