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Growth is a dynamic process influenced by many intrinsic and extrinsic factors that interplay to determine not only ultimate attained height but also the tempo and timing of increase in height. Research continues to unravel hormonal and genetic complexities that account for variations in “normal” growth, and etiologies for disordered growth. Careful tracking of childhood growth is a sensitive indicator of health and well-being, and therefore an essential component of sound pediatric care. Detection of unexplained acceleration or deceleration in growth rate or tracking along a disparate percentile considering family height genetics should prompt investigation. Endocrine disorders comprise an important, but only partial, differential diagnosis of abnormal growth. This chapter discusses essential components of normal growth, the detection and evaluation of worrisome growth, and diagnosis and treatment of its multiple etiologies. The ultimate goal is to provide for those caring for children a conceptual framework for the assessment of and diagnostic approach to the child with abnormal growth.
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Phases of Normal Growth
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The rate of linear growth and the physiologic components regulating it vary with age. Conceptually, it is helpful to define growth as occurring in four discrete but congruent phases—prenatal, infancy, childhood, and adolescence. According to the infancy-childhood-puberty growth model, phases are successive and partly superimposed. The infancy phase has been assumed to begin at mid-gestation and to tail off at approximately 2 to 3 years of age. It is regarded as being predominantly nutrition dependent. The childhood growth phase overlaps the infancy phase, begins sometime between 6 and 12 months of age, and is typically abrupt in onset. Its starting point probably defines the age at which intrauterine factors recede and growth hormone (GH) begins toexert significant influence (Figure 2-1).1 It has been shown that the timing of infancy-childhood transition is significantly associated with final adult height, and a delayed transition is the most common predictor of later idiopathic short stature (ISS).2 The transition from the childhood to puberty phase is characterized by an abrupt increase in sex hormones with a concomitant increase in GH secretion, and the contribution of the changing growth rates during puberty is reflected by the sigmoid pattern of height gain. The considerable individual variation in timing of puberty between early- and late-maturing children is depicted by brown shaded areas in Figure 2-2.
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Early detection of deviation from normal growth velocity is the key to prompt evaluation and diagnosis ...