NNN

Osteomalacia

Oct 03, 20242 min read

Osteomalacia is characterized by an inadequate mineralization of bone. The skeleton softens and weakens, causing pain, tenderness to touch, bowing of the bones, and pathologic fractures. Oh physical examination, skeletal deformities (spinal kyphosis and bowed legs) give patients an unusual appearance and a waddling gait.

Pathophysiology

  1. The major defect in osteomalacia is a deficiency of activated vitamin D. Vitamin D promotes calcium absorption from the GI Tract and facilitates mineralization of the bone.
  2. The supply of calcium and phosphate in the extracellular fluid is low and does not move to calcification sites in bones.
  3. This may result from failed calcium absorption or from excessive loss of calcium from the body (e.g. in kidney failure), GI disorders resulting in fat-soluble vitamin (D) deficiency or calcium deficiency. Liver and kidney (activators of vitamin D) disorders may also result in osteomalacia.
  4. Severe renal insufficiency (e.g. from chronic glomerulonephritis, obstructive uropathies, etc. reduce phosphate levels) produces acidosis, which the body attempts to correct by releasing skeletal calcium, resulting in bony fibrosis and cysts.
  5. Hyperparathyroidism leads to skeletal decalcification and thus osteomalacia by increasing phosphate excretion in the urine.
  6. Prolonged use of anticonvulsants (e.g. phenytoin, phenobarbital) poses a risk of osteomalacia.
  7. Most common in areas of the world where Vitamin D is not supplemented, where dietary deficiencies exist, and where sunlight is rare.

Diagnostic Examination

  • X-ray studies show evident generalized demineralization of bone. Vertebrae may show a compression fracture with indistinct vertebral end plates.
  • Laboratory studies show low serum calcium and phosphorus levels with moderately elevated ALP.
  • Urine excretion of calcium and creatinine is low.
  • Bone biopsy show increased amounts of “prebone” or osteoid, a demineralized, cartilaginous bone matrix.

Management

Physical, psychological, and pharmaceutical measures are used to relieve discomfort and pain.

  • If the underlying cause of osteomalacia is corrected, the disorder may resolve.
  • If kidney disease prevents activation of vitamin D, supplementation requires the activated form of vitamin D, calcitriol.
  • If malabsorption causes osteomalacia, vitamin D dosage is increased, with supplemental calcium.
  • Sunlight exposure may be recommended, as ultraviolet radiated transforms a cholesterol substance (7-dehydrocholesterol) found in the skin into vitamin D.
  • If osteomalacia is dietary in origin, interventions are similar to osteoporosis (lifestyle; diet, exercise).
  • Long-term monitoring is required for correction of deformities. Some persistent orthopedic deformities (e.g. in the long bones) may require braces or surgery (e.g. osteotomy) to be corrected.

Backlinks

Graph View