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INTRODUCTION

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Extremity complaints are common in children; they are estimated to account for as many as 10% of non–well-child visits to pediatricians’ offices. Conversely, rheumatologic conditions are rare, affecting fewer than 200,000 children in the United States. Thus, clinicians caring for children need an efficient and effective means of distinguishing arthritis, lupus, and other autoimmune conditions from injuries, infections, tumors, and noninflammatory causes of extremity complaints. This chapter will discuss the key components of a focused history and physical examination, the basic tools for evaluating a child with musculoskeletal symptoms. The next chapter discusses laboratory and imaging studies that may be used to confirm or refute the caregiver’s clinical suspicions.

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EPIDEMIOLOGY

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The reported incidence and prevalence of musculoskeletal diseases in children worldwide vary significantly. For example, among more than 30 epidemiologic studies of juvenile arthritis, new cases are reported to arise at a rate of 0.008 to 0.226 per 1000 children, yielding a reported prevalence of 0.07 to 4.01 per 1000 children. Although geographic, genetic, and environmental factors result in true variations in the incidence of rheumatologic conditions, several additional factors also contribute to reported differences. First among them is that most pediatric rheumatologic conditions are diagnosed on the basis of clinical criteria rather than definitive laboratory, imaging, or histopathologic findings. New signs may develop over time, leading to reclassification of conditions. Thus, children treated for ankylosing spondylitis may later develop colitis, resulting in a new diagnosis of Crohn disease–related arthritis. Arthritis that remits after several months and does not recur may be called monocyclic juvenile idiopathic arthritis by one caregiver and postinfectious arthritis by another. Despite these imprecisions inherent in a field based on clinical diagnoses, outcomes in virtually all autoimmune conditions are optimized by expeditious diagnosis and early initiation of effective therapy. Thus, classifying a child’s rheumatologic condition as accurately as possible is essential.

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PATHOPHYSIOLOGY

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The presenting symptoms of musculoskeletal conditions are more dependent on the location of the abnormality than on the specific diagnosis. Thus, fractures, tumors, and osteomyelitis all present with pain that may awaken the patient from sleep because of the constant stimulation of sensory nerves by lesions within bone. Conversely, for unknown reasons, children with arthritis seldom complain of pain. One study of more than 400 children presenting to a pediatric rheumatology clinic found that 90% of those with joint or extremity pain did not have arthritis, and more than 90% of those with arthritis did not complain of pain. Inflammatory arthritis may cause children to limp because their joints are stiff, but pain generally is absent (distinct from adults in whom arthritis is universally described as painful). Thus, differences in the location, timing, and characteristics of a child’s symptoms enable a pediatrician to rapidly narrow the potential causes of musculoskeletal complaints. Confirmation of the suspected diagnosis may then be obtained from findings on physical exam, often without need for further investigations.

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