CHAPTER 156

Juvenile Idiopathic Arthritis and Benign Joint Pains of Childhood

Miriam F. Parsa, MD, MPH, FAAP, and Deborah McCurdy, MD, FAAP

Joint pain is a common presentation in the pediatric population, and etiologies include trauma, infection, anatomic, and chronic inflammatory arthritis, such as juvenile idiopathic arthritis (JIA). Differentiating between a benign, self-limited etiology and a potentially destructive, chronic process is critical to the preservation of growing bones and cartilage. The etiology of joint pain may be roughly divided into 2 categories: mechanical and inflammatory. Mechanical or noninflammatory causes include pes planus, hindfoot valgus, and hypermobility. Inflammatory causes can be infectious, postinfectious (ie, immune complex mediated), or autoimmune mediated. Distinguishing between mechanical and inflammatory processes and determining the necessity of a pediatric rheumatology consultation may be straightforward after obtaining a detailed history and conducting a thorough physical examination and focused laboratory investigation.

Epidemiology

Juvenile idiopathic arthritis is the most common pediatric rheumatologic disease and among the more common chronic diseases of childhood. In the United States, the estimated annual incidence is 14 per 100,000 children, and the estimated prevalence is 96 per 100,000 children. The disease can occur in all racial and ethnic profiles with variable frequencies. Juvenile idiopathic arthritis is most prevalent among whites (typically oligoarticular JIA) and least prevalent in blacks and Asians. Consistent with most autoimmune diseases, females are affected more commonly than males.

Juvenile idiopathic arthritis is typically classified based on the International League of Associations for Rheumatology system. Juvenile idiopathic arthritis is an umbrella term for a set of diverse diseases with 1 common thread: chronic idiopathic inflammation of the joint space (Table 156.1). Juvenile idiopathic arthritis encompasses all of what historically was called “juvenile rheumatoid arthritis” and “juvenile chronic arthritis.” The term “rheumatoid” was removed because rheumatoid factor (RF) antibodies are absent in most children with JIA. With increased knowledge of the genetics and inflammatory pathways in each subgroup of JIA, it is likely that the JIA nomenclature will be modified to further define the disease process and increase the homogeneity of each subgroup.

Abbreviations: JIA, juvenile idiopathic arthritis; RF, rheumatoid factor.

Data derived from Petty RE, Southwood TR, Manners P, et al; International League of Associations for Rheumatology. International League of Associations for Rheumatology classification of juvenile idiopathic arthritis: second revision, Edmonton, 2001. J Rheumatol. 2004;31(2):390–392; and Cassidy JT, Laxer RM, Petty RE, Lindsley CB. Textbook of Pediatric Rheumatology. 6th ed. Philadelphia, PA: Saunders Elsevier; 2011.

Clinical Presentation

Juvenile idiopathic arthritis presents with arthritis during the disease course. Arthritis is defined as joint edema on examination or a joint or joints with both pain on range of motion and limitation of range of motion. The onset of JIA may be insidious (eg, oligoarticular), rapid (eg, RF-positive polyarticular), or variable (eg, systemic) (Table 156.1). Adolescents 16 years and older with a new diagnosis of chronic idiopathic arthritis are considered to have adult rheumatoid arthritis, not JIA. The child with JIA may be observed to limp mostly in the mornings, have difficulty completing writing assignments, or exhibit regression of gross motor milestones. Complications of JIA, such as long-standing anterior uveitis, leg length discrepancy, and joint flexion contracture, may result in difficulties performing activities of daily living and at school. Leg length discrepancy is a product of chronic inflammation providing excess blood flow to an open epiphysis (eg, most obvious is the distal femoral epiphysis), causing premature and accelerated growth with eventual premature epiphyseal closure.

Oligoarticular JIA is the most common form of JIA, with approximately 50% of all JIA cases of this type, and peaks in the second and third years of life. It is defined by the presence of arthritis in fewer than 5 joints during the first 6 months of disease and most often involves the large joints; the knee is most commonly affected, followed by the hip. A child may present with single joint involvement. Oligoarticular JIA takes persistent and extended forms, the latter associated with a more severe disease course and mimicking adult polyarticular disease. Extended oligoarthritis remains asymmetric compared with rheumatoid arthritis, which is defined by symmetric disease. Up to 50% of children with oligoarticular JIA extend to involve 5 or more joints within several years of diagnosis (ie, extended oligoarthritis).

In addition to complications, such as leg length discrepancy and joint flexion contracture, the child with oligoarticular JIA is at increased risk for developing anterior uveitis. Anterior uveitis is inflammation of the anterior uveal tract and adjacent ciliary body, and it is not clear why the same types of inflammatory cells are targeting seemingly disparate targets (eyes and joints). Anterior uveitis may be a clinically silent component of the disease course in approximately 25% of all patients with oligoarticular JIA and, in a minority of affected patients, may cause blindness. Guidelines put forth by the American Academy of Pediatrics and American Academy of Ophthalmology define risk factors and ophthalmologic screening frequencies for the prevention of JIA-associated uveitis and are based on the age of onset of JIA and presence of antinuclear antibody (ANA) (Table 156.2). Screening recommendations are relevant for all children with oligoarticular, polyarticular, psoriatic, and undifferentiated JIA.

Polyarticular JIA is defined as arthritis of 5 or more joints during the first 6 months of disease and represents approximately 30% of JIA cases. The 2 peaks of disease incidence are suggestive of 2 different genetic interplays. Rheumatoid factor-negative disease is the more common subtype, often with a positive ANA test and increased risk for anterior uveitis, with a tendency to present in early childhood. Rheumatoid factor-positive disease most commonly presents in early adolescent girls with symmetric small joint disease and carries a worse prognosis in terms of joint damage. The arthritis is erosive and, if disease is uncontrolled, may result in boutonnière deformity (ie, proximal interphalangeal joint flexion and distal interphalangeal joint hyperextension) and swan neck deformity (ie, proximal interphalangeal joint hyperextension and distal interphalangeal joint flexion). Disease complications include flexion contractures, leg length discrepancy, uveitis, and temporomandibular joint arthritis.

Systemic JIA is present in 10% to 15% of patients with JIA and is associated with the greatest morbidity and mortality of all JIA subtypes. Systemic JIA lacks the autoantibody, sex, age, and human leukocyte antigen (HLA) associations seen associated with other JIA subtypes. It is characterized by fever, rash, lymphadenopathy, hepatosplenomegaly, and serositis. Classically, fevers are quotidian or daily in pattern and are accompanied by a migratory rash that consists of discrete salmon-colored macules seen predominantly on the trunk and proximal extremities (Figure 156.1). If arthritis is among the presenting symptoms, pain is worse during the febrile period. The arthritis is typically polyarticular, affecting large and small joints, and occurs within the first 6 months of symptoms. Patients are often initially categorized as “fever of unknown origin” because arthritis may be minimal or, more often, absent at time of presentation.

Abbreviations: ANA, antinuclear antibody test; N/A, not applicable; +, positive; –, negative.

^a Recommendations for follow-up continue through childhood and adolescence.

From Cassidy J, Kivlin J, Lindsley C, Nocton J; American Academy of Pediatrics Section on Rheumatology, Section on Ophthalmology. Ophthalmologic examinations in children with juvenile rheumatoid arthritis. Pediatrics. 2006;117(5):1843–1845.

Macrophage activation syndrome is a rare but life-threatening complication of systemic JIA. Patients present with hepatosplenomegaly, lymphadenopathy, and purpura and may progress to multiorgan failure. A relative decrease in inflammatory markers (eg, erythrocyte sedimentation rate [ESR]) is observed in macrophage activation syndrome, which is in contrast to an elevation of these markers when systemic JIA exacerbates during disease exacerbation as liver and bone marrow function deteriorates. Treatment involves steroids and immunosuppressive therapy. In patients with systemic JIA, triggers to macrophage activation syndrome include viral infections and addition or change in medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), sulfasalazine, and etanercept.

Figure 156.1. Salmon-colored rash seen in systemic juvenile idiopathic arthritis with Koebner phenomenon.

Enthesitis-related arthritis is characterized by typically lower extremity arthritis and inflammation of the insertions of tendons, ligaments, fascia, and joint capsule to bone (ie, enthesitis). Unlike oligoarticular and polyarticular JIA, in which autoantibodies are frequently present (eg, ANA, RF), enthesitis-related arthritis is generally seronegative with a strong association with HLA B27. Enthesitis-related arthritis most likely represents the earliest clinical stage of spondylarthritis, which is defined by inflammatory axial disease. Juvenile ankylosing spondylitis is an example of a spondylarthritis and generally affects boys aged 8 years or older. Extra-articular symptoms include anterior uveitis, which is acute and painful, in contrast with uveitis seen in oligoarticular and polyarticular arthritis, which is initially asymptomatic.

Psoriatic arthritis occurs in patients with chronic arthritis and psoriasis or those who meet 2 of the following criteria: dactylitis, nail pitting or onycholysis, and first-degree relative with psoriasis. The age at onset is biphasic, occurring at 3 years and 11 years of age. Clinical presentation of the younger cohort is similar to oligoarticular JIA, with the exception of higher frequencies of small joint involvement and dactylitis, with a sausage-like appearance of the digit. The older cohort resembles adult psoriatic arthritis and is characterized by axial skeletal involvement and enthesitis. The arthritis, which is asymmetric, may present before the psoriatic rash, making diagnosis difficult. Similar to polyarticular JIA, the biphasic nature of psoriatic arthritis is suggestive of different genetic contributions. Up to 17% of patients have asymptomatic uveitis, similar to ANA-positive oligoarticular JIA, and require routine slit-lamp examination for diagnosis.

Abbreviations: ALL, acute lymphoblastic leukemia; EBV, Epstein-Barr virus; JIA, juvenile idiopathic arthritis; TB, tuberculosis.

^a Systemic lupus erythematosus, mixed connective tissue disease, sarcoidosis, juvenile dermatomyositis, Henoch-Schönlein purpura.

Differential Diagnosis

The differential diagnosis for joint pain in children is vast, including infectious, oncologic, immunologic, and autoimmune etiologies, and the pain can be characterized as self-limited or chronic based on a targeted history and thorough physical examination (Table 156.3) (Box 156.1). Joint pains of childhood may be self-limited in nature and include growing pains, postinfectious arthralgia, and pain amplification as well as mechanical abnormalities (eg, hypermobility syndrome) as causal.

Growing pains are a benign cause of pain in children and usually resolve within 1 to 2 years of onset (see Chapter 116). Growing pains are characterized by nocturnal pain without objective musculoskeletal manifestations. The pain generally is localized to the bilateral lower extremities and is relieved by massage, heat, or NSAIDs. The family history often is positive for growing pains. Additional workup is required in the patient with systemic symptoms (eg, fevers, weight loss), persistent pain during the day, objective musculoskeletal examination abnormalities, limping, or unilateral pain. Osteoid osteoma is a benign prostaglandin-producing bone tumor that typically involves the lower extremity, most commonly the proximal femur, and less commonly includes spinal involvement. Symptoms include unilateral, progressive pain that is worse at night, is unrelated to activity, and is improved with NSAIDs (ie, prostaglandin inhibitor). Physical examination may reveal point tenderness, edema, or muscle atrophy. Diagnosis is made using a plain radiograph or, in select cases, computed tomography.

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