Osteomalacia (adult vitamin D deficiency)
Osteomalacia is inadequate mineralization of newly formed bone, most often from severe, prolonged vitamin D deficiency due to poor intake, limited sun exposure, or malabsorption after celiac disease or gastric bypass. It causes diffuse bone pain and tenderness, proximal weakness, and pseudofractures, with elevated alkaline phosphatase, low or low-normal calcium and phosphorus, 25-hydroxyvitamin D usually below 10 ng/mL, and secondary hyperparathyroidism; treatment is vitamin D 50,000 IU weekly for 8 weeks, then daily maintenance, with calcium and correction of the underlying cause.
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What this article covers
- Overview
Definition: osteomalacia is inadequate mineralization of newly formed bone; it develops when calcium and phosphate concentrations, osteoblast function, or the conditions for mineralizing mature osteoid are inadequate.
- Epidemiology
Nutritional vitamin D deficiency is the most common cause of osteomalacia.
- Risk factors
Malabsorption, the most important acquired cause: celiac disease, gastric bypass and other bariatric surgery, inflammatory bowel disease, short-bowel syndrome, pancreatic insufficiency, and…
- Pathophysiology
Vitamin D activation: the liver converts vitamin D2 or D3 to 25-hydroxyvitamin D (calcifediol, the storage form), and the kidney converts it to 1,25-dihydroxyvitamin D (calcitriol), which stimulates…
- Clinical features
Diffuse bone pain with weight bearing or palpation is the hallmark, with bone tenderness classically at the tibial plateau and sternum, and over the ribs.
- Differential diagnosis
Bone metastases: focal hotspots on bone scan without generalized skeletal uptake, usually with hypercalcemia rather than hypocalcemia; radiography, CT, or MRI of the hotspots separates metastases from pseudofractures.
- Diagnosis
There is no formal criteria score; osteomalacia is established by the combination of the clinical picture and a characteristic biochemical pattern, and confirmed by response to treatment.
- Management
First, if hypocalcemia is severe or symptomatic (tetany, seizure, QT prolongation), give IV calcium: 10% calcium gluconate 1 to 2 g IV over 10 to 20 minutes, then a continuous infusion of 0.5 to 1.5…
- Complications
Fractures of the ribs, pelvis, and feet, and progression of pseudofractures to complete fractures, in untreated severe disease.
- Prognosis
Excellent with treatment: unlike osteoporosis, osteomalacia does not cause permanent loss of bone structure, and bone density increases substantially or normalizes after repletion.
- Prevention
Keep 25-hydroxyvitamin D at least 20 ng/mL, the level that prevents metabolic bone disease in otherwise healthy adults; this is generally met with an intake of 600 to 800 IU/day.
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- Secondary hyperparathyroidism
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- Celiac disease
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