Osteomalacia literally means "soft bones". It is a metabolic disorder that renders the skeleton less resistant, predisposes for bone pain and fractures. It is most frequently caused by vitamin D deficiency.
Both radiologic and clinical findings may prompt a suspicion for OM. Thus, the disease may be diagnosed in patients undergoing diagnostic imaging for any other reason, or in individuals that present with characteristic symptoms. Generalized bone pain as well as symmetrical bone pain localized to vertebral spine, pelvis and thighbones are frequent causes of presentation to health care givers. Arms and ribs may be affected during later stages of the disease. Bone pain may be accompanied by fatigue, proximal muscle weakness and gait disturbances. Patients often report to have difficulties to rise from a sitting or prone position, or to climb stairs. In other cases, they present with (recurrent) pathological fractures.
In plain radiographic images, reduction of bone density (osteopenia) and Looser zones (pseudofractures) are frequently detected . Vertebrae and pelvic bones may be compressed, and in severe cases, the patient's stature may progressively diminish. Alterations of spine curvature may be noted.
Symptoms largely resemble those of the more common osteoporosis and neither anamnestic data nor results of physical examination allow for a clear distinction between both bone disorders. Laboratory analyses of blood samples are very helpful to this end. Alterations of parameters like serum calcium, phosphate, pre-vitamin D, vitamin D, PTH, urea and creatinine may indicate hypocalcemia or hypophosphatemia, vitamin D deficiency, hyperparathyroidism and renal insufficiency, and thus argue for OM. Alkaline phosphatase levels are elevated in all forms of OM and osteoporosis; this parameter is highly sensitive but little specific and does neither permit to infer about the underlying disease.
In most cases, vitamin D deficiency accounts for OM. This condition is associated with hypophosphatemia, reduced concentrations of pre-vitamin D and vitamin D, and possibly hypocalcemia, whereby the latter is not an exclusion criterion. In case of hypocalcemia, PTH concentrations may be elevated and the patient may be diagnosed with secondary hyperparathyroidism.
If these measurements don't permit a definite diagnosis, calcium and phosphate excretion should be revised by analysis of a 24-hour urine sample. In case of confirmed kidney disease, the respective workup should be realized: Renal sonography and pyelography are valuable techniques, but the therapeutic approach of choice largely depends on prior findings.
Because OM occurs secondary to an underlying disease, causative treatment of OM consists in curing the respective primary disorder.
Improvement of OM-associated symptoms may be expected a few weeks after the initiation of an adequate treatment. The above mentioned blood parameters should be evaluated periodically after starting therapy. Additionally, bone mineral density tests should be performed to monitor response to therapy or disease progression. In contrast, resolution of bone deformities is not to be expected despite successful treatment.
Prognosis is generally good if the underlying disease is curable. This applies both to rickets and to adult OM; with regards to the former, bone deformations may be permanent if therapy is initiated in a delayed manner or not at all. In these cases, rickets can be associated with significant morbidity. In adult OM, skeletal deformities are usually not an issue. However, pathological fractures are, and especially in post-menopausal women, osteoporosis is not a rare comorbidity. Such a condition may considerably complicate the healing process.
Bone mineralization is an ongoing process and both bone resorption (and subsequent release of minerals into circulation) as well as deposition of hydroxyapatite take place throughout life. These processes are regulated by a complex network of mediators, with vitamin D, parathyroid hormone (PTH) and calcitonin playing important roles. OM may be considered the result of a disturbance of those regulatory mechanisms, and may either be provoked by lack of resources or deficits in resource management. In detail, the following conditions may trigger OM:
Deposition and resorption of minerals in or from osseous tissue is a permanent, physiological process. Thus, disturbances of the equilibrium between both may affect people of any age. However, bone turnover is much more pronounced in children, whose skeleton constantly has to adapt to growth and changes of force distribution. Consequently, OM is generally more severe in pediatric patients. In fact, owing to the importance of that condition for the child's development, this disease has its proper name and is called rickets. OM is thus an umbrella term for rickets and adult OM, but is more commonly used to describe the latter.
Several epidemiological studies have been conducted to ascertain vitamin D deficiency, the most common cause of OM. It has been estimated that more than half of the population aged 60 years and older is vitamin D deficient , but this disease is also highly prevalent among children . For the Western world, incidence of rickets in children aged up to three years has been reported to be approximately 6:100.000 . Less reliable data are available for the adult population, presumably because OM is rarely diagnosed before symptoms manifest.
In OM, mineralization of osseous tissues is pathologically reduced. In order to understand how bone mineralization can be disturbed, it is essential to understand which physiological events eventually lead to deposition of hydroxyapatite in the organic matrix surrounding osteoblasts and osteocytes.
Hydroxyapatite is the main component of the inorganic bone matrix and mainly consists of calcium and phosphorus. Thus, an adequate supply of both minerals is essential for bone mineralization. Furthermore, the ratio of calcium and phosphorus significantly affects the availability of either electrolyte. In detail, low calcium:phosphorus levels, i.e., dietary restriction of phosphorus supply, have been shown to exacerbate demineralization.
Calcium and phosphorus have to be absorbed in the gastrointestinal tract and excessive renal excretion has to be prevented by reabsorption. On the other hand, appropriate measures need to be taken to avoid an overload with those electrolytes. Accordingly, regulation of serum levels of calcium and phosphorus depend on a variety of factors:
Consequently, any pathological condition that results in vitamin D deficiency, hyperparathyroidism, or - at least theoretically - lack of calcitonin, may induce OM. In practice, the relative importance of the three aforementioned disorders decreases in the order stated.
As has been described above, vitamin D deficiency is the main cause of OM. However, PTH levels are not independent of serum concentrations of vitamin D. In fact, low levels of vitamin D stimulate PTH release. Thus, an individual who suffers from vitamin D deficiency may eventually develop secondary hyperparathyroidism .
Patients should be advised about maintaining a healthy, balanced diet. While nutritional deficiencies may be detrimental, excess supplementation of certain nutrients may have similar effects. Indeed, vitamin D is lipophilic and an overdose may have fatal consequences . Dietary supplementation of vitamin D should not exceed 600 international units (IU) per day in patients aged 1 to 70 years. This also applies for pregnant and lactating women. Young infants may be prescribed 400 IU per day; people who are older than 70 years may ingest 800 IU daily. If at all possible, serum levels of vitamin D should be maintained in the range of 30 to 60 ng/ml.
Lack of exposure to sunlight and use of sunblock even though solar irradiation is low impair endogenous synthesis of vitamin D. Covering of the whole body, as frequently seen in Muslim women, has repeatedly been shown to increase the risk for bone disorders like OM.
Osteomalacia (OM) is a metabolic bone disease characterized by inadequate mineralization of osseous tissue. Function of osteoblasts, osteocytes and osteoclasts as well as the composition of the organic bone matrix is unaltered. In contrast, imbalances between bone formation and bone resorption account for the different entity osteoporosis.
Although OM may be diagnosed in patients pertaining to all age groups, it is not a congenital condition in the narrow sense of the word. It may be present in children, and is effectively known as rickets in such cases, but as per definition, it is an acquired disease. OM may, however, manifest as a complication of hereditary disorders.
The most common cause of OM is vitamin D deficiency, which, in turn, may result from insufficient dietary supply, malabsorption and disturbances of endogenous vitamin D synthesis. Furthermore, disturbances of calcium and phosphorus homeostasis may provoke OM.
Chronic pain, muscle weakness and pathological fractures are the most common signs of OM, and diagnosis is often delayed until such symptoms manifest. Identification of the underlying disorder is of utmost importance to treat the disease. The outcome largely depends on the primary disorder and the extent of bone deformations, if present.
Osteomalacia (OM) literally means "soft bones" and is a metabolic disorder that renders the skeleton less resistant, predisposes for bone pain and fractures. It is caused by disturbances in the bone mineralization.
The most common trigger of OM is vitamin D deficiency. Vitamin D plays an important role in maintaining calcium homeostasis and if vitamin D levels are below certain thresholds, the intestinal absorption of calcium is considerably reduced. If calcium is not provided, bones cannot be mineralized. Other causes of OM include lack of exposure to sunlight, disorders of the parathyroid glands and the kidneys.
Affected individuals often claim bone pain and muscle weakness, or report to have difficulties to rise from a sitting or prone position, or to climb stairs. Their susceptibility to fractures is increased and in fact, OM may not be diagnosed until a patient presents with a fractured bone.
Therapy consists in treating the underlying disease. Thus, in most cases, dietary supplementation of vitamin D, possible also of phosphate and calcium, may be recommended. However, overdosage may have detrimental effects. Thus, all patients should talk to their treating physicians about the necessary dose of nutrients in their particular case.