Osteomalacia is a bone disease characterized by the loss of mineral content, which is diffuse in nature. This acquired condition primarily affects adults and is marked by defects in the mineralization of the bone’s protein matrix.
The main cause is a deficiency of vitamin D, leading to soft bones that are prone to deformation and fractures.
The Role of Vitamin D in the Body’s Skeletal System
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| Image of osteomalacia (Photo: TTO) |
Vitamin D, which is fat-soluble, exists mainly in two forms: vitamin D2 found in yeast and vitamin D3 synthesized in human skin when exposed to sunlight (ultraviolet rays), and is primarily found in fish liver oil and egg yolk. Milk is rich in both forms of vitamin D. The synthesis in the skin is the primary source of vitamin D.
Vitamin D acts as a prohormone, producing various metabolites that function like hormones. Its main role is to enhance calcium absorption from the intestine and facilitate normal bone formation and mineralization. Specifically, in bones, vitamin D stimulates osteoblasts to produce more alkaline phosphatase and osteocalcin (a vitamin K-dependent bone protein), while producing less collagen, all of which favor bone formation.
Main Causes of Osteomalacia
Osteomalacia can occur due to insufficient vitamin D supply, metabolic disorders of vitamin D, or tissue insensitivity to it. It is commonly seen in the elderly who have limited sun exposure or diets deficient in vitamin D. Osteomalacia can also be caused by malabsorption of vitamin D through the digestive tract or metabolic disorders such as gastric bypass, intestinal resection, chronic intestinal diseases, pancreatic and biliary disorders, malabsorption syndrome, renal failure, or parathyroid gland dysfunction.
It is important to note that some medications taken in high doses for a prolonged period can cause osteomalacia, such as anticonvulsants (phenobarbital, phenytoin), fluoride, bisphosphonates (etidronate), and aluminum-containing antacids (aluminum hydroxide).
Additionally, phosphate metabolism disorders can also lead to osteomalacia (phosphate diabetes). For example, Fanconi syndrome, a renal tubular disorder, causes excessive phosphate excretion through the kidneys, resulting in hypophosphatemia.
Vitamin D deficiency leads to reduced calcium absorption through the digestive system, hypocalcemia, secondary hyperparathyroidism, and impaired mineralization of bone tissue. De-mineralization occurs, particularly in the spine, pelvis, and lower limbs. Due to soft bones, body weight can cause bending of long bones, compression fractures of vertebrae, flattening of the pelvis, leading to a narrowed pelvic inlet.
Diagnosis of Osteomalacia
Clinically, osteomalacia should be considered in the following situations:
– Diffuse bone pain and tenderness upon palpation, with hip pain affecting gait. Pain may occur in the pelvis, chest, scapula, spine, starting as dull and progressively becoming persistent and frequent.
– Impaired mobility due to pain and decreased muscle strength in the limbs, gait disturbances, waddling gait, or even bed-ridden status.
– Bone deformities and fractures in late stages. Osteomalacia may be suggested when fractures occur after minimal trauma.
– Tetany seizures caused by rickets due to hypocalcemia.
Patients require X-rays of affected bones to detect characteristic signs such as diffuse osteopenia, combined with loss of trabecular bone and cortical thinning, as well as Looser-Milkmann lines.
Laboratory tests may show hypocalcemia, hypophosphatemia, low vitamin D levels, hyperparathyroidism, elevated alkaline phosphatase in the blood, and reduced urinary calcium.
Thus, clinical symptoms, laboratory tests indicating changes in serum calcium, alkaline phosphatase levels, 25(OH)D3 levels, and X-rays can confirm the diagnosis of osteomalacia. Additionally, it is necessary to identify the underlying cause of osteomalacia. Vitamin D deficiency is the most common cause, while medication-related causes should not be overlooked. Less commonly, phosphate metabolism disorders are responsible.
Treatment of Osteomalacia
Patients with osteomalacia need vitamin D supplementation. Treatment is done in cycles, depending on the cause and severity of the disease. It is important to note that 1 mcg of vitamin D is equivalent to 40 International Units (IU). In cases of osteomalacia due to vitamin D deficiency, vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol) should be administered at doses of 800-4,000 IU daily for 6-12 weeks, followed by a maintenance dose of 200-600 IU. Older adults may require up to 50,000 IU weekly for 8 weeks to treat vitamin D deficiency.
Osteomalacia due to malabsorption requires higher doses of vitamin D, possibly up to 100,000 IU per day, in conjunction with calcium (calcium carbonate 4g/day). For patients taking anticonvulsants, additional vitamin D is necessary. Calcitriol (0.25-1 mcg taken four times a day) is effective for treating hypocalcemia or osteodystrophy due to chronic renal failure. Additionally, it is essential to discontinue any medications that may cause osteomalacia and supplement phosphate if there are phosphate metabolism disorders.
