Planning the treatment of a patient who has rickets.

Abstract

Only a growing child, prior to fusion of the epiphyses, can develop rickets, which is characterized by poor mineralization of epiphyseal cartilage and consequent growth retardation. Several circumstances result in clinical rickets, including inadequate dietary intake of vitamin D, inadequate exposure to ultraviolet rays in sunlight to form endogenous vitamin D, acquired or inherited disorders of vitamin D metabolism, inherited renal tubular defects that produce hypophosphatemia or acidosis, hereditary resistance to the final metabolite of vitamin D (dihydroxycholecalciferol), and chronic administration of anticonvulsants.Appropriate levels of both calcium and phosphorous are essential for optimal bone mineralization. Although calcium homeostasis is controlled in the intestines, phosphate homeostasis is regulated in the kidneys. Vitamin D is generated initially either by ingestion in the diet or by endogenous production in the skin following ultraviolet irradiation. It is transported to the liver where it is hydroxylated to 25(OH)D or hydroxycholecalciferol, which in turn circulates to the kidneys and undergoes further hydroxylation to 1,25(OH)2D or dihydroxycholecalciferol. This final metabolite is the most active form of the vitamin and acts on the intestinal lumen to enhance calcium and phosphorous absorption as well as on the renal tubules to increase phosphorous reabsorption. A derangement at any level of calcium/phosphorous homeostasis can result in rickets. Nutritional vitamin D deficiency accounts for the majority of rickets in underdeveloped countries today, but non-nutritional causes are encountered much more frequently in developed nations such as the United States as a direct result of effective vitamin D supplementation. However, it is important to remember that nutritional rickets does occur in the United States, especially among dark-skinned infants born during the winter months who are exclusively breastfed without receiving vitamin D supplements.Clinical manifestations of rickets generally occur in the latter half of the first year and during the second year of life. Signs include craniotabes (softening of the skull with a ping-pong ball sensation on pressing firmly), rachitic rosary at the costochondral junctions, Harrison groove (an indentation caused by the diaphragm pulling on the softened lower ribs), thickening of the wrists and ankles, bowlegs or knock-knees, abnormal spinal curvatures (scoliosis, kyphosis, or lordosis), coxa vara (narrower angle between the femoral neck and shaft), pelvic deformities, frequent fractures, delayed dentition, enamel defects, hypotonia, muscle weakness, and short stature. Extreme hypocalcemia may produce tetany, laryngeal spasm, and seizures. Roentgenographic features are demonstrated at the wrist, where there is cupping, fraying, and widening of the distal ends of the radius and ulna. There is also a widened gap between the distal ends of these bones and the metacarpals that results from undercalcification of the metaphyses.Early treatment of rickets is essential to minimize bony deformities and growth retardation. Treatment usually involves the administration of vitamin D, although sunlight and ultraviolet irradiation are therapeutic. Vitamin D can be replaced with oral administration of 2,000 to 5,000 IU (0.05 to 0.125 mg) of vitamin D2 (ergocalciferol) daily for 6 to 12 weeks, followed by a maintenance dose of 400 IU (0.01 mg) a day. Response to therapy can be demonstrated radiographically within 2 to 4 weeks of the onset of treatment. A lack of response to this regimen suggests an underlying etiology other than nutritional deficiency or inadequate exposure to sunlight, and treatment must be tailored to the particular condition.Children who have renal failure usually are treated with 1,25(OH)2D rather than vitamin D2; doses range from 0.01 to 0.05 mcg/kg each day. Familial hypophosphatemia requires therapy with oral phosphate in addition to a vitamin D analog to counteract secondary hyperparathyroidism. Oral phosphate is given every 4 hours in doses ranging from 0.5 to 4 g/d, depending on the age of the child. Treatment for tetany includes the oral administration of calcium chloride or calcium lactate along with milk. Alternatively, calcium gluconate can be given intravenously in instances where oral medication is contraindicated. In addition, patients receiving anticonvulsant therapies may need to have their medications discontinued. If this is not possible, doses varying from 4,000 IU (0.10 mg) to 40,000 IU (1.0 mg) daily may be necessary, with monitoring of serum calcium and vitamin D levels and of radiographs for evidence of healing.Philip O. Ozuah, MD Albert Einstein College of Medicine-Montefiore Medical Center Bronx, NYComment: As a disease of the growing skeleton, rickets can affect only children. Those of us whose epiphyses already have closed, including our older adolescent patients, also can suffer the consequences of inadequate vitamin D, but our disorder then is called osteomalacia, literally “softening of the bones.”It probably also is worth remarking that with our increasing awareness of the danger that unabated sunlight poses to our skin and the resulting increased use of suncreens to block ultraviolet rays, we all should be sure to have an adequate source of vitamin D in our diets.Henry M. Adam, MD Editor, In Brief