Osteomalacia is a bone disorder characterized by the replacement of normal mineralized bone by osteoid as a result of a defective skeletal mineralization of the bone matrix.
The bones are soft, due to abnormalities in the metabolism of vitamin D and/or phosphate.
When the disorder appears in childhood, there is also an impaired mineralization of the growth cartilage and the newly formed bone and it is called rickets.
The main causes of osteomalacia are:
Vitamin D is necessary for a normal bone mineralization because it increases the absorption of calcium and phosphate and maybe because it also plays a major role in the proliferation of osteoblasts.
Osteomalacia, due to lack of vitamin D may have multiple causes:
In general, the clinical signs of osteomalacia are very subtle. In fact, it is possible to detect osteomalacia histologically in the absence of symptoms.
When there are symptoms related the most common one is the bone pain. It is usually a dull pain and more intense in the weight-bearing bones (lumbar spine and lower extremities, such as the hip and knee, during standing and walking).
On examination, pain may be triggered when the bone is pressed (pressure on the rib cage or pelvis) or struck (tibia).
The second most common symptom is muscle weakness, that usually affects the shoulder and pelvic girdle.
In more serious cases, fractures of the bones with a low bone density may occur. In addition, in an x-ray test there may be evidence of areas called “Looser-Milkman”, radiolucent zones or bands in cortical bone that are described as pseudofractures.
There is no change in the EMG (electromyogram) or in the biopsy.
The classical pattern of osteomalacia due to lack of vitamin D is hypocalcemia (low level of calcium in the blood), hypophosphatemia (low level of phosphorus in the blood) and high alkaline phosphatase. However, the elevation of calcium and phosphorus in the blood usually are discrete or non-existent.
A specific test is the measure of plasma 1,25-dihydroxyvitamin D where the level is usually over 30 ng/ml. However, this test is only recommended in patients with vitamin D deficiency and not like a routine test.
The differential diagnosis should exclude:
In a simple X-Ray, areas of bones with decalcification or deformities can be seen, especially in children. It usually affects the tibia and the femur with angular deformities.
The most specific feature, although not frequently seen, are the Looser-Milkman lines.
The vertebral bodies show a biconcave deformation uniformly throughout the spine. If other deformities are present, they can be also detected.
In any case, the X-ray usually does not show any abnormal sign.
It is necessary to know the underlying cause to give a proper treatment.
If the cause is a vitamin D deficiency it is advisable to increase the exposure to sunlight to at least 30-40 minutes each day, preferably between 10 a.m. to 3 p.m. and/or prescribe vitamin D supplements (in the form of calcitriol, cholecalciferol) and calcium.
In addition, a diet rich in vitamin D is recommended. Vitamin D can be found in fish, mushrooms, shrimps, dairy products, fortified cheeses and tuna.
In patients with vitamin D deficiency or with a high risk to develop it, vitamin D supplements may be used. For example, patients over 60 years of age, with little or no sun exposure, obese people or postmenopausal women.