Bone thinning disorders

Osteoporosis

Description

• Trabecular thinning and perforation with loss of interconnecting bridges, with continued aging, cortical bone also becomes involved.

  

Causes

• Most common cause
  • ↑ Bone resorption (↑ osteoclast number and activity) due to factors like low estrogen levels, old age, cigarette smoking.
• Secondary causes
  • Drugs (e.g., steroids, alcohol, anticonvulsants, anticoagulants, thyroid replacement therapy, PPI)
  • Conditions (e.g., hyperparathyroidism, hyperthyroidism, multiple myeloma, malabsorption syndromes, anorexia).
  • Low BMI (or weight)
  • Prolonged microgravity exposure (eg, space travel)
• UWT of medications associated with osteoporotic fractures

<aside> 🧩

Perimenopausal woman with fragility fracture→ Check drug history.

</aside>

<aside> 🧠

PPI (omeprazole) decreases Ca absorption which leads to osteoporosis.

</aside>

Diagnosis

• Fragility fracture (e.g., fall from standing height, minimal trauma).
• Radiology
  • Bone mineral density measurement by DEXA (dual-energy x-ray absorptiometry).
    • Sites of measurement→ lumbar spine, total hip, and femoral neck.
    • Diagnostic score→ T-score of ≤ −2.5
• Lab values
  • Normal serum Ca²⁺ and PO₄³⁻

<aside> 💡

One-time screening recommended for females ≥ 65 years old.

</aside>

Complications

• Overlay

• Vertebral compression fractures

  • Acute back pain
  • Loss of height
  • Kyphosis

• Femoral neck fracture

• Distal radius (Colles) fracture

Treatment

• Bisphosphonates
• Teriparatide
• SERMs (selective estrogen receptor modulators)
• Denosumab (monoclonal antibody against RANKL)
• Romosozumab (sclerostin inhibitor)

Prophylaxis

• Regular weight-bearing exercise
• Adequate Ca²⁺ and vitamin D intake throughout adulthood.

• Overlay

Osteomalacia/Rickets

Pathogenesis

• Vitamin D deficiency leads to ****defective mineralization of
  • Osteoid in adults→ osteomalacia
  • Cartilaginous growth plates in children→ rickets

Presentation in children with rickets

• Pathologic bow legs (genu varum)
• Beadlike costochondral junctions (rachitic rosary)
• Craniotabes (soft skull)

Diagnosis

• X-ray Findings
  • Osteomalacia
    • Osteopenia
    • Pseudofractures.
  • Rickets
    • Epiphyseal widening
    • Metaphyseal cupping/fraying.
• Laboratory Findings
  • ↓ Vitamin D → ↓ serum Ca²⁺ → ↑ PTH secretion → ↓ serum PO₄³⁻
  • Hyperactivity of osteoblasts→ ↑ serum ALP.

Types of rickets

• Rickets can be categorized as calcipenic (low calcium) or Phosphopenic (low phosphorus).
  1. Calcipenic rickets can be due to
     • Low calcium intake
     • Deficiency or metabolic disorders (eg, receptor defects) of vitamin D.
  2. Phosphopenic rickets mostly due to
     • Primary defect in renal phosphate reabsorption (eg, hereditary hypophosphatemic rickets)

• Other pictures

Bone thickening disorders

Osteopetrosis

Description

• Inherited defect of bone resorption resulting in abnormally thick, heavy bone that fractures easily.

Pathophysiology

• Mutations (e.g., carbonic anhydrase II) impair osteoclast ability to generate acidic environment for bone resorption→ thickened, dense bones prone to fracture.

Presentation

• Bone fractures
• Overgrowth of cortical bone fills marrow space→ pancytopenia and extramedullary hematopoiesis.
• Cranial nerve impingement due to narrowed foramina→ Vision and hearing impairment.

Diagnosis

• X-ray
  • Diffuse symmetric sclerosis (bone-in-bone, "stone bone").
• Histology

Treatment

• Bone marrow transplant is potentially curative as osteoclasts are derived from monocytes.

Osteitis Deformans (Paget Disease of Bone)

Description

Lab Values in Bone Disorders (Top HY)