Juvenile Idiopathic Arthritis

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Chapter 149 Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) (formerly juvenile rheumatoid arthritis) is the most common rheumatic disease in children and one of the more common chronic illnesses of childhood. JIA represents a heterogeneous group of disorders all sharing the clinical manifestation of arthritis. The etiology and pathogenesis of JIA are largely unknown, and the genetic component is complex, making clear distinction among various subtypes difficult. As a result, several classification schemas exist, each with its own limitations. In the Classification Criteria of the American College of Rheumatology (ACR), the term juvenile rheumatoid arthritis (JRA) is utilized and categorizes disease into 3 onset types (Table 149-1). Attempting to standardize nomenclature, The International League of Associations for Rheumatology (ILAR) proposed use of a different classification using the term juvenile idiopathic arthritis (JIA) (Table 149-2), which is inclusive of all subtypes of chronic juvenile arthritis. We refer to the ILAR classification criteria; enthesitis-related arthritis and psoriatic JIA are covered in Chapter 150 (Tables 149-3 and 149-4).

Table 149-2 CHARACTERISTICS OF THE AMERICAN COLLEGE OF RHEUMATOLOGY (ACR) AND INTERNATIONAL LEAGUE OF ASSOCIATIONS FOR RHEUMATOLOGY (ILAR) CLASSIFICATIONS OF CHILDHOOD CHRONIC ARTHRITIS

PARAMETER ACR (1977) ILAR (1997)
Term Juvenile rheumatoid arthritis (JRA) Juvenile idiopathic arthritis (JIA)
Minimum duration ≥6 wk ≥6 wk
Age at onset <16 yr <16 yr
≤4 joints in 1st 6 mo after presentation • Pauciarticular
>4 joints in 1st 6 mo after presentation • Polyarticular
Fever, rash, arthritis • Systemic • Systemic
Other categories included Exclusion of other forms
Inclusion of psoriatic arthritis, inflammatory bowel disease, ankylosing spondylitis No (Chapter 150) Yes

Table 149-3 INTERNATIONAL LEAGUE OF ASSOCIATIONS FOR RHEUMATOLOGY CLASSIFICATION OF JUVENILE IDIOPATHIC ARTHRITIS (JIA)

CATEGORY DEFINITION EXCLUSIONS
Systemic-onset JIA
Oligoarticular JIA
Polyarthritis (RF-negative) Arthritis affecting ≥5 joints during the 1st 6 mo of disease; a test for RF is negative. a, b, c, d, e
Polyarthritis (RF-positive) Arthritis affecting ≥5 joints during the 1st 6 mo of disease; ≥2 tests for RF at least 3 mo apart during the 1st 6 mo of disease are positive. a, b, c ,e
Psoriatic arthritis Arthritis and psoriasis, or arthritis and at least 2 of the following: b, c, d, e
1. Dactylitis.  
2. Nail pitting§ and onycholysis.  
3. Psoriasis in a 1st-degree relative.  
Enthesitis-related arthritis Arthritis and enthesitis,| or arthritis or enthesitis with at least 2 of the following: a, d, e
   
Undifferentiated arthritis Arthritis that fulfills criteria in no category or in ≥2 of the above categories.  

RF, rheumatoid factor.

* Quotidian fever is defined as a fever that rises to 39°C once a day and returns to 37°C between fever peaks.

Serositis refers to pericarditis, pleuritis, or peritonitis, or some combination of the three.

Dactylitis is swelling of ≥1 digits, usually in an asymmetric distribution, that extends beyond the joint margin.

§ A minimum of 2 pits on any one or more nails at any time.

| Enthesitis is defined as tenderness at the insertion of a tendon, ligament, joint capsule, or fascia to bone.

Inflammatory lumbosacral pain refers to lumbosacral pain at rest with morning stiffness that improves on movement.

From Firestein GS, Budd RC, Harris ED Jr, et al, editors: Kelley’s textbook of rheumatology, ed 8, Philadelphia, 2009, Saunders/Elsevier.

Pathogenesis

JIA is an autoimmune disease associated with alterations in both humoral and cell-mediated immunity. T lymphocytes have a central role, releasing proinflammatory cytokines (e.g., TNF-α, IL-6, and IL-1). The cytokine profile favors type 1 helper T-lymphocyte response. Studies of T-cell receptor expression confirm recruitment of T lymphocytes specific for synovial non-self antigens. Complement consumption, immune complex formation, and B-cell activation also promote inflammation. Inheritance of specific cytokine alleles may predispose to upregulation of inflammatory networks, resulting in systemic-onset disease or more severe articular disease.

Systemic-onset JIA may be more accurately classified as an autoinflammatory disorder, more like familial Mediterranean fever (FMF), than the other subtypes of JIA. This theory is supported by work demonstrating similar expression patterns of a phagocytic protein (S100A12) in SoJIA and FMF, as well as the same marked responsiveness to IL-1 receptor antagonists.

All these immunologic abnormalities cause inflammatory synovitis, characterized pathologically by villous hypertrophy and hyperplasia with hyperemia and edema of the synovial tissue. Vascular endothelial hyperplasia is prominent and is characterized by infiltration of mononuclear and plasma cells with a predominance of T lymphocytes (Fig. 149-1). Advanced and uncontrolled disease leads to pannus formation and progressive erosion of articular cartilage and contiguous bone (Figs. 149-2 and 149-3).

image

Figure 149-3 MRI with gadolinium of a 10 yr old child with juvenile rheumatoid arthritis (same patient as in Fig. 149-1). The dense white signal in the synovium near the distal femur, proximal tibia, and patella reflects inflammation. MRI of the knee is useful to exclude ligamentous injury, chondromalacia of the patella, and tumor.

Clinical Manifestations

Arthritis must be present for a diagnosis of any subtype of JIA to be made. Arthritis is defined by intra-articular swelling or the presence of 2 or more of the following signs: limitation in range of motion, tenderness or pain on motion, and increased heat or erythema. Initial symptoms may be subtle or acute and often include morning stiffness with a limp or gelling after inactivity. Easy fatigability and poor sleep quality may be associated. Involved joints are often swollen, warm to touch, and painful on movement or palpation with reduced range of motion but usually are not erythematous. Arthritis in large joints, especially knees, initially accelerates linear growth, causing the affected limb to be longer and resulting in a discrepancy in limb lengths. Continued inflammation stimulates rapid and premature closure of the growth plate, resulting in shortened bones.

Oligoarthritis is defined as involving ≤4 joints within the first 6 mo of disease onset, predominantly affecting the large joints of the lower extremities, such as the knees and ankles (Fig. 149-4). Often only a single joint is involved. Isolated involvement of upper extremity large joints is less common. Those in whom disease never develops in more than 4 joints are regarded as having persistent oligoarticular JIA, whereas evolution of disease in more than 4 joints over time changes the classification to extended oligoarticular JIA. The latter often portends a worse prognosis. Involvement of the hip is almost never a presenting sign and suggests a spondyloarthropathy (Chapter 150) or nonrheumatologic cause. The presence of a positive antinuclear antibody (ANA) test result confers increased risk for asymptomatic anterior uveitis, requiring periodic slit-lamp examination (Table 149-5).

Polyarthritis (polyarticular disease) is characterized by inflammation of ≥5 joints in both upper and lower extremities (Figs. 149-5 and 149-6). When rheumatoid factor (RF) is present, polyarticular disease resembles the characteristic symmetric presentation of adult rheumatoid arthritis. Rheumatoid nodules

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