Raquitismo

SYMPOSIUM: METABOLIC MEDICINE

Rickets
Paul Dimitri Nick Bishop

Abstract
Worldwide, rickets is the most common form of metabolic bone disease in children. Despite the concept that it is a rare disease, it is on the increase in many regions, including Western Europe and the USA, and in many ethnic subgroups that have immigrated to temperate regions. Vitamin D deficiency is the main cause ofrickets, though nutritional deficiency of calcium and phosphorous generates the same clinical picture. Rickets also occurs when the metabolites of vitamin D are deficient. This may be due to an inherited cause or secondary to disorders of the gut, pancreas, liver or kidney from disruption of vitamin D metabolism.

Keywords 1,25-dihydroxyvitamin D; 25-hydroxyvitamin D; hypophosphataemic rickets;osteomalacia; rickets; vitamin D; vitamin D-dependent rickets

Clinical features
Accelerated changes in body composition, bone growth and dental development during infancy and adolescense,1 associated with an increase in calcium and phosphate demands,2,3 exaggerate the detrimental affects of vitamin D deficiency. This is particularly important in adolescence, when peak bone mass is achieved.4,5Rickets typically presents at 4–18 months of age in nutritional vitamin D deficiency and X-linked hypophosphataemic rickets (XLH). Preterm infants develop rachitic changes from 7 weeks of age if their diet is inadequate. The clinical signs of calcium deficiency rickets occur up to 2 years later. Vitamin D deficiency during adolescence usually results in osteomalacia. Skeletal effects of vitamin Ddeficiency The earliest radiological sign is the loss of demarcation between the growth plate and the metaphysis. This progresses until the classical radiological features of rickets (metaphyseal cupping, fraying and splaying (Figure 1a) best seen at the wrists, knees or ankles) are evident. The widening of the space between the epiphysis and the metaphysis is due to expansion of the layer of hypertrophicchondrocytes in the growth plate. As healing begins, a thin white

line of calcification appears at the junction of the growth plate and the metaphyseal area that becomes denser and thicker as calcification proceeds. Unmineralised osteoid causes the periosteum to appear separated from the diaphysis. Osteomalacia appears on radiography as generalised osteopenia with visible coarsening oftrabeculae due to secondary hyperparathyroidism. Once the child is walking, bowing of the legs due to tibial and femoral softening occurs (Figures 1b and 2). Genu varum with an intercondylar distance of more than 5 cm is suggestive of rickets and is the commonest bony deformity in infants and young children; genu valgum and windswept deformities are more often seen in older cases. Diffuse bone pain is afeature of both rickets and osteomalacia. Through prolonged mechanical stress on softened vertebrae in severe rickets, kyphoscoliosis may develop in children over the age of 2 years. The anteroposterior diameter of the pelvis can shrink resulting in a ‘triradiate’ or ‘flat’ pelvis. These changes may cause obstructed labour with associated maternal and infant morbidity. The costochondral junctionsbecome swollen after 1 year of age, leading to an appearance termed ‘rickety rosary’. The development of Harrison’s groove and pectus carinatum result from muscles pulling on weakened bones. Cartilaginous swellings are also evident in a bracelet conformation around the wrist and the ankles. The main distinction is from normal-sized wrist bones that become more prominent secondary to muscle wasting inmalnourished children. Craniotabes is softening of the skull bones due to failure of intramembranous ossification.6 It is usually seen in early infancy, and may occur before 2 months age in nutritionally deficient preterm babies. Although present in rickets, it is not pathognomonic of this disorder.7 Expansion of the cranial vault relative to the facial skeleton causes frontal bossing. This...