Infantile osteomalacia: Description, Causes and Risk Factors:
Both calcium and phosphorus are essential components of bone mineral, and any significant disruption in the metabolism of either or both elements affects the modeling or remodeling of bone. Vitamin D is a crucial factor in this metabolism because it directly affects the ability of the small intestine to absorb these elements. It is thus important in the homeostatic mechanisms by which concentrations of calcium and phosphorus in serum are maintained at optimal concentrations. A lack of vitamin D prevents the mineralization of bone protein (osteoid). During growth, bone devoid of mineral is unable to support biomechanical function and deformity occurs. After growth has ceased the potential effect of vitamin D deficiency is less serious. However, remodeling of bone continues and prolonged deficiency of vitamin D can result in deformity as mineralized bone is replaced by unmineralized osteoid. This can be particularly severe in special circumstances such as pregnancy when the needs of the developing baby are met at the expense of the mother.Infantile osteomalacia is a systemic disease of early childhood that extensively affects the skeleton, but has no direct mortality. Precursors of vitamin D contained in food are transformed through the influence of the ultraviolet fraction of sunlight. This explains the prevalence of infantile osteomalacia in populations climatically (high latitudes) or mechanically (crowded cities, occlusive clothing) deprived of direct exposure to sunlight. However, it should be appreciated that human groups with darker skin pigment are vulnerable even in tropical sunshine, because most of the ultraviolet rays are absorbed by the skin's melanin pigment. The main causative factor of infantile osteomalacia remains the inadequate intake of vitamin D and its precursors, but other genetic problems in mineral absorption and retention can produce similar changes in the human skeleton.The skeletal changes observed in infantile osteomalacia result from three mechanisms: (l) direct effects of the metabolic disturbance, (2) deformities secondary to the vulnerability and pliability of the poorly mineralized skeleton, and (3) retardation of growth.There are several intestinal malabsorption syndromes that can result in infantile osteomalacia. Both genetic and acquired problems contribute to these syndromes. They can be caused by decreased absorption or increased fecal loss of vitamin D and probably calcium. Infantile osteomalacia can also be caused by defects in the ability of the kidneys to recycle phosphate. These results in systemic hypophosphatemia and leads to deficiencies in mineralization of osteoid. Growth disturbances can be associated with some variants of this manifestation of infantile osteomalacia. The plastic deformity associated with this type of infantile osteomalacia results in changes in the skeleton that are similar to the vitamin D deficiencyThe manifestations are earliest seen and most marked on the rapidly growing areas of the skeleton: osteocartilaginous junctions of the ribs, the distal metaphysis of the femur, radius, and ulna, and the proximal humerus. The changes at the growth plate consist of a failure to mineralize the columnar cartilage and the osteoid newly deposited on the cartilage septae. Because the proliferation of cartilage and the formation of bone matrix by osteoblasts continues at close to normal levels, both unmineralized cartilage, which can-not be resorbed, and unmineralized osteoid accumulate next to the growth plate. In the ribs this results in a rounded nodular swelling of the osteocartilaginous junction, the "rachitic rosary," and in long bones, results in a broadening and cup-shaped depression of the metaphyseal areas. Where as intramembranous bone formation and endochondral formation are affected equally, the rapidly growing and expanding cranial vault of the infant increasingly is replaced by non-mineralized osteoid, which gives rise to areas of thinning and softening (craniotabes). This actually precedes recognition of the changes in the long bones in acute infantile osteomalacia.Symptoms:
Signs and symptoms related to particular organ may include:Skull: In active infantile rickets the cranial vault may develop thin and soft areas, especially in the posterior lateral portions of the parietal bones and of the occipital squama (craniotabes). This is due to rapid remodeling of the infant skull to accommodate the growing brain, replacing mineralized bone with osteoid. This is not to be confused with the incomplete ossification of the entire cranial vault in pre-mature infants or with the congenital lacunar skull that often complicates spina bifida, in which sharply marginated multiple defects in various areas of the cranial vault are present. Craniotabes may lead to permanent posterior flattening or lateral and asymmetrical deformities of the skull, due to pressure of the head against the supporting surface in the prone position. Closure of the fontanels is delayed in rickets. In cases where longstanding thickening of the cranial vault is seen, especially in older children, mainly due to external (occasionally also internal) sub-periosteal bone deposition, the external deposition often spares the center of the parietal
and frontal tubera. Similar subperiosteal deposits can occur on the facial bones.Long Bones: The frequent combination of hypovitaminosis
D and general malnutrition leads to a combination of infantile osteomalacia and osteoporosis, resulting in a porotic form of infantile osteomalacia characterized by brittle thin cortex and sparse cancellous trabeculae. ln otherwise well-nourished infants, however, the deposition of massive amounts of osteoid on endosteal and periosteal surfaces results in the plump bones, which have narrowed medullary spaces, that are characteristic of the hyper plastic form of rickets. In the porotic form, stress fractures, especially in the diaphysis lead to axial deformities.Although growth is slowed down in active infantile osteomalacia, the development of secondary epiphyseal ossification centers is not delayed. The most marked shortening is seen on the femur. The most characteristic change of a long bone is the flaring of the frayed metaphyseal cortex and cupping of the end of the metaphysis. Periosteal deposition of osteoid, which is mineralized in the healing process, is common. Generally, these deposits are thickest at mid-diaphysis, giving the shaft the appearance of a column, without the usual tapering to the middle. These subperiosteal bone deposits show a characteristic distribution in different bones. On the ribs, they are limited to the anterior surface and the margins, leaving the pleural surface free. Deposits are heavier on the posterior than on the anterior surface. On the tibia, the deposits locate on the posterior and on the medial surface, leaving free the lateral surface that faces the fibula.Ribs: The ribs may show flattening of their curves secondary to bending of the rib cartilage at the costochondral junction. This leads to a forward bending of the sternum, giving the pigeon breast deformity (pectus carinatum). In severely malacic infantile osteomalacia, lateral depression of the rib contour may occur secondary to the pressure of the arms. The reduced or absent mineralization in infantile osteomalacia results in an abnormal accumulation of osteoid in the growing ends of bones including the ribs, where this is particularly apparent at the costochondral junction. At this site the rib ends enlarge, forming the lumpy appearance in the chest wall known as the rachitic rosary.Vertebrae: In severe infantile osteomalacia, the vertebral bodies may have decreased height due to compression, often combined with a deeper scalloping of the endplate. Although kyphoscoliosis may develop after infantile osteomalacia, major abnormal curvatures are usually lacking in the active phase.Pelvis: The pelvis is more affected by altered growth than by mechanical deformation. The typical rachitic pelvis, during the active disease, is smaller and plumper than normal, but does not show the disproportions of the adult post rachitic pelvis. The typical post rachitic flat pelvis is characterized by an anteroposterior narrowing of the pelvic canal, mainly due to deficiency of growth of the iliac portion of the pelvic ring. The maximal growth period of this portion, especially from its posterior growth cartilage, falls into the infant period and is not made up later, whereas the maximal growth of the pubic bones falls into later childhood and adolescence. Therefore, the transverse diameter of the pelvic canal is not diminished and the pelvis appears flattened. Posteriorly, the transverse diameter of the sacrum is not significantly affected. The sacrum tends to protrude more into the pelvic canal and the acetabulum face more forward than normal. Because unmineralized tissues are rarely preserved in archeological human burials, some of the features of active infantile osteomalacia are not present in archeological skeletons. However, if recovery occurs, some mineralized deformities will be preserved.Diagnosis:
It may be suspected from the child's medical history, symptoms, or lifestyle. Blood can be tested for vitamin D and calcium levels. Also, blood tests for liver function may show changes linked to rickets. A bone X-ray (usually of the wrist bones) is often done. This can show changes due to rickets (and needs only a very small amount of X-rays).A physical exam reveals tenderness or pain in the bones, rather than in the joints or muscles.The following tests may help diagnose rickets:Arterial blood gases.
- Blood tests (serum calcium).
- Bone biopsy (rarely done).
- Bone x-rays.
- Serum alkaline phosphatase.
- Serum phosphorus.
Other tests and procedures include the following:ALP (alkaline phosphatase) isoenzyme.
- Calcium (ionized).
- PTH (parathyroid hormone).
- Urine calcium.
Vitamin D deficiency rickets findings:Low- normal serum calcium level.
- Increased secretion of PTH (secondaryhyperparathyroidism) to compensate for low calcium.
- Hyperparathyroidism will increase renal excretion ofphosphate, leads to low serum phosphate level
- Elevated alkaline phosphatase enzyme.
- Reduced urinary calcium level.
- Low level of both 25 and 1, 25-dihydroxyvitamin D.
- Elevated parathyroid hormone level.
Hypophosphatemic rickets findings:Low serum phosphate level.
- Normal calcium level.
- Normal parathyroid hormone level.
- High alkaline phosphatase level.
- In-appropriate low or normal 1,25-dihydroxyvitamin D.
The goals of treatment are to relieve symptoms and correct the cause of the condition. The cause must be treated to prevent the disease from returning. Replacing calcium, phosphorus, or vitamin D that is lacking will eliminate most symptoms of rickets. Dietary sources of vitamin D include fish, liver, and processed milk. Exposure to moderate amounts of sunlight is encouraged.Vitamin D supplements: This is generally taken as a form of vitamin D called ergocalciferol or calciferol. The vitamin D is given in high doses, in order to improve the rickets quickly.Vitamin D can be taken as liquids, tablets or injections. The liquids/tablets can be taken on a daily, weekly or monthly basis, depending on the dose needed and on which option is preferred. If injections are used, they are not needed very often. For example, the first two doses could be given a month apart, followed by a repeat injection every six months.If lack of calcium is part of the problem, calcium supplements can also be taken. These can be liquids or tablets. If calcium levels are severely low and causing problems, calcium can be given by an infusion (a 'drip') in hospital.NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.