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also have polyarthritis or arthralgia, colicky abdominal pain, and nephritis As with the rash, periarticular swelling usually involves joints below the waist Chronic arthritis is less common than acute arthritis in children younger than age 16 years, with an incidence of 20 to 150 cases per 100,000 JIA is a newer term used to classify chronic childhood arthritis This term describes children less than 16 years of age with joint inflammation for at least weeks, in whom other causes have been eliminated, and encompasses all of the diseases referred to as JRA, as well as other causes of idiopathic arthritis Subclassifications of disease are based on the patient’s age at onset of symptoms, duration and pattern of arthritis, and presence or absence of systemic signs such as fever or rash Tests for rheumatoid factor or ANA may assist in establishing a specific diagnosis Since JIA has a highly variable presentation, it appears at many different points in the diagnostic algorithm These are difficult diagnoses for ED clinicians to establish based on a single patient encounter Children with chronic arthritis should be referred to a rheumatologist (see Chapter 101 Rheumatologic Emergencies ) In the absence of fever, chronic pain of one or more joints may also indicate malignancy Specifically, leukemia or neuroblastoma can both present with true joint swelling, as can bony tumors Pallor, adenopathy, weight loss, and other constitutional complaints, as well as anemia or cytopenias, would support this diagnosis A large joint oligoarthritis occurs as an extraintestinal complication of inflammatory bowel disease in about one-third of children, usually during times of active disease Clues to the diagnosis include abdominal pain, hematochezia, anemia, and weight loss In summary, this review of joint pain in children should serve as a guide to the diagnostic evaluation The clinician must choose from many different causes, each with variable and nonspecific characteristics In addition, laboratory studies are rarely specific for a particular disease However, by asking the appropriate questions, performing a careful physical examination, selectively obtaining adjunct studies, and developing pattern recognition skills, the clinician can follow the correct diagnostic path Suggested Readings and Key References Bachur RG, Adams CM, Monuteaux MC Evaluating the child with acute hip pain (“irritable hip”) in a Lyme endemic region J Pediatr 2015;166(2):407– 411 Caird MS, Flynn JM, Leung YL, et al Factors distinguishing septic arthritis from transient synovitis of the hip in children A prospective study J Bone Joint