Osteomalacia16,17

GENERAL PRINCIPLES

• Osteomalacia is characterized by defective mineralization of osteoid. Bone biopsy reveals increased thickness of osteoid seams and decreased mineralization rate, assessed by tetracycline labeling.

• Suboptimal vitamin D nutrition, indicated by plasma 25-hydroxy vitamin D (25[OH]D) levels lt;30 ng/mL, is very common and contributes to the development of osteoporosis.

• Etiology

î Dietary vitamin D deficiency

î Malabsorption of vitamin D and calcium because of intestinal, hepatic, or biliary disease

î Disorders of vitamin D metabolism (e.g., renal disease, vitamin D-dependent rickets)

î Vitamin D resistance

î Chronic hypophosphatemia

î Renal tubular acidosis

î Hypophosphatasia

DIAGNOSIS

Clinical Presentation

• Clinical findings include diffuse skeletal pain, proximal muscle weakness, waddling gait, and propensity to fractures.

• Osteomalacia should be suspected in a patient with osteopenia, elevated serum alkaline phosphatase, and either hypophosphatemia or hypocalcemia.

Diagnostic Testing

• Serum alkaline phosphatase is elevated. Serum phosphorus, calcium, or both may be low.

• Serum 25(OH)D levels may be low, establishing the diagnosis of vitamin D deficiency or malabsorption.

• Radiographic findings include osteopenia and radiolucent bands perpendicular to bone surfaces (pseudofractures or Looser zones). Bone density is decreased.

TREATMENT

• Dietary vitamin D deficiency can initially be treated with ergocalciferol 50,000 international units (IU) PO weekly for 8 weeks to replete body stores, followed by long-term therapy with cholecalciferol 2000 IU#8725;d.

• Malabsorption of vitamin D may require continued therapy with high doses such as 50,000 IU PO per week. The dose should be adjusted to maintain serum 25(OH)D levels above 30 ng#8725;mL. Calcium supplements, 1 g PO daily, tid, may also be required. Serum 25(OH)D and serum calcium should be monitored every 6-12 months to avoid hypercalcemia.