Osteomalacia is a dysfunction of bone mineralization. It is much less common than osteoporosis and can only be definitively diagnosed through bone biopsy. The clinical syndrome that is associated with the disease consists of fractures, pain, and myopathy.
In older adults, the most common cause of osteomalacia is vitamin D deficiency due to inadequate intake. In addition, the excessive use of antacids, some of which bind to phosphate, can cause osteomalacia. The chronic use of anticonvulsants, malabsorption syndromes, chronic renal failure, and hepatobiliary disease may result to osteomalacia.
The use of high-dose etidronate and fluoride may contribute to the development of osteomalacia. A characteristic waddling gait may also arise, primarily as a result of hip pain and thigh weakness.
Laboratory studies typically show elevated levels of alkaline phosphatases, low or normal calcium, and low phosphate. Examination through plain radiographs may show osteopenia or even characteristic pseudofractures. These are most commonly seen in the proximal femur.
The treatment of osteomalacia depends on the underlying cause. If the diagnosis involves vitamin D deficiency, oral supplementation of vitamin D 1000 IU per day can accomplish repletion. On the other hand, if the cause is hypophosphatemia, the use of neutral phosphate salts may be done. Osteomalacia is a disease that involves the weakening of the bones due to failed mineralization.
The symptoms of osteomalacia are not specific. In adults, osteomalacia does not present with any skeletal abnormalities. However, patients with osteomalacia often complain of a bone discomfort that is throbbing in character. These patients often note that bone discomfort is worse when lying down in bed or sitting. Another feature of osteomalacia is that it causes proximal muscle weakness as well as aching.
The disease is characterized by pain, which is sometimes severe, in the pelvic bones, lower back, and legs. Tenderness may also be felt in the shin and other bones. The characteristic gait of patients with osteomalacia is that they walk with their feet wide apart and they appear to waddle. Deformities of the pelvic bone may become obvious. An involuntary twitching of the face, known as tetany, may also occur. Another feature is the presence of spontaneous fractures. Before the deformities are clinically relevant, diagnosis can be made through x-ray, which should show decalcification or rarefaction of bones all over the body. Osteomalacia should not be confused with osteoporosis, which also features decalcification.
The causes of osteomalacia vary, but it is often caused by vitamin D deficiency.
Vitamin D deficiency leads to hypocalcemia, which leads to osteomalacia in adults and rickets in children. When a person becomes vitamin D deficient, there is a decrease in the efficiency of intestinal calcium absorption, and this subsequently causes a decrease in ionized calcium. This is recognized by the parathyroid gland, which then releases parathyroid hormone (PTH) to conserve calcium by increasing its resorption in the distal convoluted tubules of the kidneys. Thus, unless there is no longer any calcium in the bones, the blood level of calcium remains fairly constant. Only when the skeleton is completely depleted of calcium will hypocalcemia be observed.
Vitamin D deficiency occurs because of a number of reasons. One is that there may be conditions that interfere with the absorption of vitamin D in the body.
These disorders include Crohn’s disease, which is an intestinal disorder. There are also conditions which prevent the body from activating or producing vitamin D.
These include kidney disorders, liver diseases, and hypoparathyroidism.
Diets lacking in vitamin D are also prime causes of osteomalacia. Not enough vitamin D in the diet can lead to reduced vitamin D circulation in the body, which prevents calcium from circulating in the bloodstream.
Not enough exposure to sunlight is another cause of osteomalacia. This commonly affects individuals who are always indoors for prolonged periods of time due to advanced age, illness, or disability. In addition, infants in tropical countries are often swaddled in clothes and are exposed to too little sun.
Having dark skin is another problem because it prevents the skin from absorbing sunlight, which negates its effects on vitamin D metabolisms. Certain drugs can cause osteomalacia, such as drugs used to treat epilepsy and seizures. Anticonvulsants have been implicated in osteomalacia. Rarely, tumors can cause osteomalacia.
Risk factors for osteomalacia are varied. One risk factor is being dark-skinned. Certain ethnicities are more prone to osteomalacia because they cannot adequately absorb sunlight through their skin, which is needed for the metabolism of vitamin D.
Another risk factor is the consumption of aluminum antacids. Studies show that patients who were being dialyzed with water that contained a high level of aluminum subsequently developed osteomalacia. At lower concentrations, aluminum stimulates osteoblastic activity. At higher concentrations, however, it inhibits the release of PTH, as well as inhibiting osteoblastic activity. It is also deposited on the surfaces of bones, preventing the mineralization of the skeleton.
Heavy fluoride intake has also been associated with osteomalacia. At lower concentrations, fluoride stimulates osteoblastic activity, while at higher concentrations, it stimulates osteoblastic activity and becomes incorporated into the skeleton. Certain populations in the world that consume large amounts of fluoride but have diets deficient in calcium develop skeletal deformities.
The consumption of drugs that inhibit vitamin D absorption is another risk factor.
Children and adults who are on several anti-seizure medications often exhibit osteomalacia or rickets. Glucocorticoids, St. John’s wort, and medications used to treat HIV also cause osteomalacia.
Low levels of vitamin D in men may place them at an increased risk for cancers, particularly digestive system cancers. This effect is more prominent in men.
Vitamin D deficiency may also worsen atherosclerosis and increases vascular morbidity and mortality.
Vitamin D deficiency, in addition to these, also increases the vulnerability to severe infections, as well as increasing the mortality for critically ill patients.
Stress fractures and spontaneous fractures are also common complications of osteomalacia. Low blood calcium level, as well as chronic pain, are other complications.
Low levels of calcium in the blood can lead to hypocalcemia. Hypocalcemia is a difficult condition that may cause confusion, depression, and memory loss.
The symptoms of extreme hypocalcemia include tingling in hands and feet, muscle aches, difficulty breathing, and muscle twitches. It may also cause abnormal heart rhythm.
The diagnosis of osteomalacia rests on adequate biochemical testing. This should include measurements of levels of ionized calcium, which may be normal or low, PTH (which may be normal or high), and vitamin D, which is usually found to be less than 50 nmol/L.
When serum alkaline phosphatase is slightly raised, this can be a sensitive marker for the mineralization effect of osteomalacia. Most laboratories report the total alkaline phosphatase level. Although there are specific assays for bone alkaline phosphatase, osteomalacia is generally diagnosed when alkaline phosphatase is raised but other liver enzymes remain normal.
Treatment comprises replacement with vitamin D replacement and calcium supplementation. Dietary calcium may be effective in some instances. However, it is easier to consume the proper amount of calcium by taking it in tablet form.
The tablet form of calcium may be calcium carbonate or calcium citrate.
Vitamin D replacement is usually in the form of ergocalciferol, which is given two to three 1000 IU capsules a day. Vitamin D replacement is appropriate even when sunlight is available. Lower doses of vitamin D are available in several over-the-counter forms. Calcitriol is the active form of vitamin D and can be used if the patient has impaired renal function.
Prevention of osteomalacia rests on having an adequate intake of vitamin D and calcium.
It is better to supplement these from the diet than to take measures to treat osteomalacia.
Adequate exposure to sunlight is also recommended for children and adults.
Sunlight activates vitamin D in the system and is essential for obtaining vitamin D.
If the patient is elderly, severely sick, or disabled, vitamin D supplementation is recommended.
It is recommended that enriched or fortified milk and milk products be consumed, as well as herring, salmon, shrimp, and sardines. These are high in calcium. Fortified cereal is another option, which can be consumed during breakfast. Cod liver oil and egg yolks are other foods rich in vitamin D and calcium.
All infants between the ages of 6 months to 5 years should be given a daily supplement of vitamin D in the form of vitamin drops.
The prognosis of those with osteomalacia is good, provided that treatment is initiated as soon as possible. Both the symptoms and the vitamin levels generally respond well to treatment. However, it can take a few months before other symptoms, such as pain, improve. Vitamin D deficiency is linked to other illnesses, such as cardiovascular and infectious disorders. This does not mean, however, that all people with vitamin D deficiency will get these problems. Nor does it mean that if a person has any of these problems, vitamin D is the cause. In these cases, vitamin D deficiency is just one factor.