Giampiero I. Baroncelli

Quantitative Ultrasound Methods to Assess Bone Mineral Status in Children: Technical Characteristics, Performance, and Clinical Application

Measurement of bone mineral status may be a useful tool in identifying the children who could be exposed to an increased risk of osteoporosis in adulthood. Dual energy x-ray absorptiometry and peripheral quantitative computed tomography may be used to this purpose, but the exposure to ionizing radiation is a limiting factor for preventive studies in large populations of children. In the last years, quantitative ultrasound (QUS) methods have been developed to assess bone mineral status in some peripheral skeletal sites such as calcaneus, phalanges of the hand, and tibia. QUS techniques are safe, easy to use, radiation-free, and devices are portable, so that they are particularly indicated to assess bone mineral status in children. This review will concentrate on the main methodological principles of ultrasounds and the QUS variables derived from their application to bone tissue, technical differences and performance of QUS methods, factors influencing QUS measurements, normative data and results obtained in children with disturbances of growth or affected by disorders of bone and mineral metabolism, including the assessment of fracture risk, and comparison among QUS, dual energy x-ray absorptiometry, and peripheral quantitative computed tomography methods.

Bone quality assessment by quantitative ultrasound of proximal phalanxes of the hand in healthy subjects aged 3-21 years

Bone quality by quantitative ultrasound was assessed in 1083 (587 males) healthy white subjects aged 3–21 y. Amplitude-dependent speed of sound (AD-SoS) through the distal end of the first phalanx diaphysis of the last four fingers of the hand was measured by an ultrasound device (DBM Sonic 1200, IGEA, Carpi, Italy). Mean AD-SoS values increased progressively from 3 to 21 y (males, 1845.9–2119.1 m/s, p < 0.0001; females, 1842.3–2098.8 m/s, p < 0.0001). They did not differ (p = NS) between sexes up to age 11, but females showed higher (p < 0.05 –p < 0.0001) AD-SoS values than males in age groups 12, 13, and 14 y. There was no difference (p = NS) of AD-SoS values between sexes in pubertal stages 1, 2, and 5, but females had higher mean AD-SoS values than males in stages 3 (p < 0.01) and 4 (p < 0.001). Independent predictors of AD-SoS were weight, body mass index, pubertal stage, and mean width of fingers in males, and age, pubertal stage, and mean width of fingers in females (p < 0.01 –p < 0.0001). However, 7.8% in males and 3.6% in females of the increment of AD-SoS values can be related to the finger anatomy alone. AD-SoS values probably reflect the architectural organization of growing bone or changes in bone elasticity. Increased bone density and size may be additional factors influencing AD-SoS. Measurement of AD-SoS at the hand phalanxes may be a simple, noninvasive, and radiation-free technique to assess bone quality in children.

Pubertal changes in biochemical markers of growth.

Puberty is a crucial period of life during which dramatic hormonal changes induce notable modifications in linear growth, bone mass and body composition. These changes are associated with variations in some biochemical parameters such as markers of bone turnover and leptin, which may reflect changes in bone growth and fat mass, respectively. Children with growth hormone (GH) deficiency have reduced concentrations of bone markers, which increase during GH administration, while the levels of leptin decrease. There have been few studies analysing the behaviour of bone markers during puberty in GH-treated GH-deficient patients and no studies analysing the behaviour of leptin. Results from a longitudinal study showed that there was no change in serum osteocalcin, carboxy-terminal propeptide of type I procollagen, and cross-linked carboxy-terminal telopeptide of type I collagen levels during puberty in GH-treated GH-deficient children. Some studies have shown that changes in markers of bone turnover and leptin after short-term GH treatment may predict the growth response (at 6–12 months) to GH administration in GH-deficient children. At present, insufficient data are available for the clinical use of these parameters as markers of growth response during pubertal development and as predictors of long-term growth response to GH treatment in children with GH deficiency. Nevertheless, the use of more and possibly new markers might improve the accuracy of growth prediction models in the future.

Assessment of bone quality by quantitative ultrasound of proximal phalanges of the hand and fracture rate in children and adolescents with bone and mineral disorders

Bone quality by quantitative ultrasound and fracture rate were assessed in 135 (64 males) children and adolescents aged 3-21 y with bone and mineral disorders such as chronic anticonvulsants or glucocorticoids treatment, juvenile rheumatoid arthritis, celiac disease, paucity of intrahepatic bile ducts, autoimmune hepatitis, genetic diseases, idiopathic juvenile osteoporosis, disuse osteoporosis, β-thalassemia major, survivors of acute lymphoblastic leukemia, liver transplantation, calcium deficiency, and nutritional or X-linked hypophosphatemic rickets. Amplitude-dependent speed of sound through the distal end of the first phalangeal diaphysis of the last four fingers of the hand was measured by an ultrasound device. In the majority of patients cortical area to total area ratio by metacarpal radiogrammetry (n=120) and lumbar bone mineral density (BMD) by dual-energy x-ray absorptiometry (n=99) were also assessed. In patients with X-linked hypophosphatemic rickets radial BMD by single-photon absorptiometry instead of lumbar BMD was measured. Mean values of amplitude-dependent speed of sound, cortical area to total area ratio, lumbar BMDarea, or lumbar BMD corrected for bone sizes estimated by a mathematical model (BMDvolume), as well as mean values of radial BMD in patients with X-linked hypophosphatemic rickets, expressed as z score, were significantly reduced (p < 0.0001) in comparison with their reference values (−1.7 ± 1.0, −2.0 ± 0.9, −3.0 ± 1.3, −1.9 ± 1.0, −2.7 ± 0.7, respectively). A positive relationship was found between amplitudedependent speed of sound and cortical area to total area ratio (r = 0.90, p < 0.0001), lumbar BMDarea (r = 0.62, p < 0.0001), or lumbar BMDvolume (r = 0.66, p < 0.0001). Fifty-two patients (38.5%) had suffered fractures in the 6 mo preceding the bone measurements, the radial distal metaphysis being the most frequent fracture site (28.8%). Mean values of amplitude-dependent speed of sound, cortical area to total area ratio, lumbar BMDarea, or lumbar BMDvolume, expressed as z score, of fractured patients were significantly lower (p < 0.0001) than those of fracture-free patients (−2.2 ± 1.0 and −1.4 ± 0.8, −2.6 ± 0.9 and −1.7 ± 0.7, −3.5 ± 1.2 and −2.5 ± 1.0, −2.5 ± 1.0 and −1.3 ± 0.7, respectively). Phalangeal quantitative ultrasound may be a useful method to assess bone quality and fracture risk in children and adolescents with bone and mineral disorders.

Bone demineralization in cystic fibrosis : Evidence of imbalance between bone formation and degradation

Bone turnover, collagen metabolism, and bone mineral status were investigated in 59 patients with cystic fibrosis and in 72 sex- and age-matched control subjects. In all patients and control subjects serum concentrations of osteocalcin (OC), carboxy-terminal propeptide of type I procollagen (PICP), amino-terminal propeptide of type III procollagen(PIIINP), and cross-linked carboxy-terminal telopeptide of type I collagen(ICTP), and urinary values of cross-linked N-telopeptides of type I collagen (NTX), as well as total body bone mineral content (TBBM) were measured. Higher ICTP (μg/L) and NTX (bone collagen equivalent/urinary creatinine (nmol/mmol) values were found in prepubertal, pubertal, and young adult patients than in control subjects (ICTP: 15.4 ± 2.1 and 13.2± 1.8, p < 0.001; 23.3 ± 5.3 and 20.1 ± 4.1,p < 0.02; 4.8 ± 1.1 and 4.0 ± 1.0, p < 0.05, respectively; NTX: 1047.5 ± 528.6 and 227.8 ± 71.8,p < 0.01; 997.8 ± 391.7 and 376.3 ± 91.0,p < 0.01; 993.2 ± 398.0 and 73.9 ± 28.5,p < 0.01, respectively). Lower OC and PICP levels (μg/L) were showed in pubertal patients in comparison with control subjects (OC: 20.2± 12.3 and 39.0 ± 15.1, p < 0.01; PICP: 305.8± 130.4 and 436.2 ± 110.1, p < 0.02, respectively). Lower OC and higher PIIINP levels (μg/L) were found in young adult patients than in control subjects (OC: 4.4 ± 3.0 and 7.0 ± 3.1,p < 0.05; PIIINP: 4.8 ± 1.1 and 3.1 ± 1.0,p < 0.001, respectively). TBBM (z score) was reduced in prepubertal, pubertal, and young adult patients (-0.8 ± 0.4, -1.0± 0.4, -1.1 ± 0.5, respectively). Patients with cystic fibrosis have bone demineralization and imbalance between bone formation and degradation.

Osteoporosis in Children and Adolescents: Diagnosis, Risk Factors, and Prevention

Bone mass acquired during childhood and adolescence is a key determinant of adult bone health. Peak bone mass, which is achieved in late adolescence, is a main determinant of osteoporosis in adulthood. Therefore, any factor adversely impacting on bone acquisition during childhood or adolescence can potentially have long-standing detrimental effects on bone health predisposing to osteoporosis and fracture risk. Thus, osteoporosis can well have its origin in childhood and adolescence. Pediatricians should be playing an active role in osteoporosis diagnosis and prevention. It is increasingly recognized that osteoporosis may occur in some disorders of children and adolescents. In this paper we review the diagnostic criteria of osteopenia/osteoporosis by densitometric assessment of bone mineral density, the contributing factors, and the mechanisms whereby several disorders may affect the acquisition of bone mass in children and adolescents. Finally, some recommendations to optimize peak bone mass in order to prevent osteopenia/osteoporosis are suggested.

Osteoporosis in children and adolescents: etiology and management

Bone mass increases progressively during childhood, but mainly during adolescence when approximately 40% of total bone mass is accumulated. Peak bone mass is reached in late adolescence, and is a well recognised risk factor for osteoporosis later in life. Thus, increasing peak bone mass can prevent osteoporosis.The critical interpretation of bone mass measurements is a crucial factor for the diagnosis of osteopenia/osteoporosis in children and adolescents. To date, there are insufficient data to formally define osteopenia/osteoporosis in this patient group, and the guidelines used for adult patients are not applicable. In males and females aged <20 years the terminology ‘low bone density for chronologic age’ may be used if the Z-score is less than −2. For children and adolescents, this terminology is more appropriate than osteopenia/osteoporosis. Moreover, the T-score should not be used in children and adolescents.Many disorders, by various mechanisms, may affect the acquisition of bone mass during childhood and adolescence. Indeed, the number of disorders that have been identified as affecting bone mass in this age group is increasing as a consequence of the wide use of bone mass measurements. The increased survival of children and adolescents with chronic diseases or malignancies, as well as the use of some treatment regimens has resulted in an increase in the incidence of reduced bone mass in this age group.Experience in treating the various disorders associated with osteoporosis in childhood is limited at present. The first approach to osteoporosis management in children and adolescents should be aimed at treating the underlying disease. The use of bisphosphonates in children and adolescents with osteoporosis is increasing and their positive effect in improving bone mineral density is encouraging. Osteoporosis prevention is a key factor and it should begin in childhood. Pediatricians should have a fundamental role in the prevention of osteoporosis, suggesting strategies to achieve an optimal peak bone mass.

Long-term growth hormone treatment in children with renal hypophosphatemic rickets : effects on growth, mineral metabolism, and bone density

OBJECTIVE To evaluate the effects of treatment with recombinant human growth hormone (rhGH) on growth, mineral metabolism, and bone density in children with renal hypophosphatemic rickets (RHR). DESIGN Long-term rhGH treatment combined with conventional therapy with 1,25-dihydroxyvitamin D3 plus inorganic phosphate salts. SETTING Endocrine unit, department of pediatrics, university hospital. SUBJECTS Twelve patients (5 boys; age range 4.6 to 12.5 years, median 7.0 years) were subdivided into two groups of six patients on the basis of the median of height z score (-2.41) and the median bone age/statural age (BA/SA) ratio (1.23). Group A included patients with a severe degree of short stature (height z score -3.4 +/- 0.5) (mean +/- SD) and altered BA/SA ratio (1.26 +/- 0.08); group B included patients with a lesser degree of short stature (height z score -2.1 +/- 0.6, p < 0.001 vs group A) and more normal BA/SA ratio (1.04 +/- 0.15, p < 0.01 vs group A). INTERVENTION Group A received rhGH treatment (0.6 IU/kg per week subcutaneously) combined with conventional therapy; group B received conventional therapy alone. MEASUREMENTS Height, growth velocity, predicted adult height, serum values of calcium, phosphate, bone alkaline phosphatase isoenzyme, osteocalcin, propeptides of type I and type III procollagen, intact parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and urinary calcium/urinary creatinine ratio and tubular maximum for phosphate reabsorption normalized to the glomerular filtration rate (TmP/GFR), as well as radial bone density, were measured at baseline and for 3 years. RESULTS Height z score, growth velocity z score, predicted adult height, serum values of phosphate, bone alkaline phosphatase isoenzyme, osteocalcin, propeptides of type I and type III procollagen, intact parathyroid hormone 1,25-dihydroxyvitamin D, and TmP/GFR, as well as radial bone density, improved significantly only in group A. Serum calcium and 25-hydroxyvitamin D, and urinary calcium/urinary creatinine ratio did not change in either group. CONCLUSIONS Long-term rhGH administration may benefit growth, phosphate retention, and bone density in patients with RHR, without evidence of side effects.

Serum levels of carboxyterminal propeptide of type I procollagen in healthy children from 1 st year of life to adulthood and in metabolic bone diseases

Type I collagen is the major component of bone matrix; circulating carboxyterminal propeptide of type I procollagen (P-I-CP) levels reflect type I collagen synthesis in tissues and may be an useful index to investigate bone metabolism. We measured P-I-CP by a new radioimmunoassay in 300 healthy children and adolescents and in 40 healthy adults to provide reference data for P-I-CP values. In addition, 79 patients with diagnosed disorders of phospho-calcium metabolism (rickets, vitamin D deficient and vitamin D resistant, hyperparathyroidism, hypo- and pseudo-hypoparathyroidism, osteopenia) were evaluated. In the healthy subjects, serum P-I-CP values were higher in children than in adults; variations of P-I-CP levels were observed according to age and sexual maturation: higher values were found in the first years of life and during pubertal development; pubertal increase reflects the different timing of pubertal development in the two sexes. P-I-CP levels were increased in primary hyperparathyroidism and reduced in diseases related to impaired secretion or action of parathyroid hormone. Higher P-I-CP levels were found in vitamin D deficient and vitamin D resistant rickets. P-I-CP was reduced in anorexia nervosa and during chronic glucocorticoid treatment while it was increased in thyrotoxic osteoporosis. In idiopathic juvenile osteoporosis, P-I-CP values ranged from reduced to increased values. We conclude that P-I-CP may represent an additional biochemical marker of bone metabolism. Since age-related variations are present, reference data for the various ages are need for clinical application of this assay.

From Bone Biology to Bone Analysis

Bone development is one of the key processes characterizing childhood and adolescence. Understanding this process is not only important for physicians treating pediatric bone disorders, but also for clinicians and researchers dealing with postmenopausal and senile osteoporosis. Bone densitometry has great potential to enhance our understanding of bone development. The usefulness of densitometry in children and adolescents would be increased if the physiological mechanisms and structural features of bone were given more consideration in the design and interpretation of densitometric studies. This review gives an overview on the most relevant techniques of quantitative noninvasive bone analysis. Furthermore it describes the relationship between bone biology, selected surrogates describing the biological processes and the possibilities of measuring these surrogates specifically and precisely by the different devices. The overall recommendation for researchers in this field is to describe firstly the biological process to be analyzed (bone growth in length, remodeling or modeling, or all together), secondly the bone parameter which describes this process, and thirdly the reason for selecting a special device.