Pediatric Rheumatology: Juvenile Idiopathic Arthritis

• Pediatric rheumatology is a subspecialty focusing on diagnosing and managing rheumatic diseases in children and adolescents.
• Rheumatic diseases are autoimmune and inflammatory, affecting joints, muscles, bones, and internal organs.
• Pediatric rheumatologists are trained to recognize the unique manifestations of these diseases in children and the differences in treatment compared to adults.

Juvenile Idiopathic Arthritis (JIA)

• Juvenile Idiopathic Arthritis (JIA) defines the most common chronic rheumatic disease in children.
• JIA is arthritis of unknown cause, starting before age 16 and lasting at least 6 weeks.
• JIA is diverse, featuring varied clinical presentations, genetic factors, and prognoses.
• The exact cause of JIA is unknown, likely a mix of genetic predisposition and environmental factors.

Classification of JIA

• The International League of Associations for Rheumatology (ILAR) has set classification criteria for JIA.
• ILAR criteria rely on clinical features in the first 6 months of the illness.
• ILAR classification includes subtypes of systemic arthritis, oligoarthritis (persistent/extended), polyarthritis (RF negative), polyarthritis (RF positive), psoriatic arthritis, enthesitis-related arthritis, and undifferentiated arthritis.

Systemic Arthritis

• Systemic arthritis involves arthritis with or preceded by fever (at least 2 weeks), plus one of: fleeting rash, generalized lymphadenopathy, hepatomegaly/splenomegaly, or serositis.
• Systemic JIA accounts for around 10% of JIA cases.
• Systemic JIA affects males and females equally.
• Systemic features may appear weeks or months before arthritis.

Oligoarthritis

• Oligoarthritis is arthritis in one to four joints during the first 6 months.
• This is the most common JIA subtype, about 50% of cases.
• Persistent oligoarthritis means arthritis stays limited to ≤4 joints through the disease.
• Extended oligoarthritis means arthritis involves >4 joints after the initial 6 months.
• Oligoarthritis is more common in girls than boys.
• The knee is the joint most often affected.
• Patients are at risk for uveitis, eye inflammation, which can cause blindness if not treated.

Polyarthritis (RF Negative)

• Polyarthritis (RF negative) is arthritis in five or more joints within the first 6 months, with a negative rheumatoid factor (RF) test.
• It accounts for approximately 20-30% of JIA cases.
• Polyarthritis (RF negative) can occur at any age.
• Generally, girls are more affected than boys.

Polyarthritis (RF Positive)

• Polyarthritis (RF positive) is arthritis in five or more joints within the first 6 months, plus a positive rheumatoid factor (RF) test.
• It is less common than RF-negative polyarthritis.
• Polyarthritis (RF positive) shows similarities to adult rheumatoid arthritis.
• Typically affects adolescent girls.
• This subtype usually has a more aggressive course.

Psoriatic Arthritis

• Psoriatic arthritis involves arthritis and psoriasis, or arthritis plus two of: dactylitis (entire digit swelling), nail pitting/onycholysis, or a family history of psoriasis in a first-degree relative.
• Psoriatic arthritis makes up a small portion of JIA cases.
• Diagnosis can be hard, as psoriasis might not be present when arthritis begins.

Enthesitis-Related Arthritis

• Enthesitis-related arthritis is arthritis and enthesitis (inflammation where tendons/ligaments attach to bone), or arthritis/enthesitis plus two of: sacroiliac joint tenderness/inflammatory spinal pain, HLA-B27 antigen presence, arthritis onset in a male after age 6, acute anterior uveitis, or family history of HLA-B27 associated disease in a first-degree relative.
• This form is more common in boys than girls.
• Lower extremity joints are more commonly affected.

Undifferentiated Arthritis

• Undifferentiated arthritis is arthritis that doesn't fit any other JIA subtype criteria, or fits more than one.
• It accounts for a small percentage of JIA cases.

Clinical Manifestations of JIA

• JIA's clinical presentation changes with the subtype.
• Common symptoms include joint pain/swelling/stiffness, limping/movement difficulty, fatigue, fever, rash, eye inflammation (uveitis), and growth disturbances.
• Joint pain often worsens in the morning or after rest.
• Affected joints might be warm to the touch and tender when touched.

Diagnosis of JIA

• JIA diagnosis relies on clinical findings, as no single test exists.
• Diagnostic criteria require ruling out other conditions causing arthritis in children, like infections, malignancy, and other autoimmune diseases.
• Lab tests help support the diagnosis and classify the JIA subtype, including complete blood count (CBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP) antibodies, antinuclear antibodies (ANA), and HLA-B27.
• Imaging, like X-rays, ultrasound, and MRI, can evaluate joints and assess inflammation/damage extent.

Treatment of JIA

• Goals of JIA treatment are to relieve pain, reduce inflammation, prevent joint damage, preserve joint function, and maintain growth/development.
• The treatment is tailored to the JIA subtype, disease severity, and patient factors.
• Treatment options: nonsteroidal anti-inflammatory drugs (NSAIDs), disease-modifying antirheumatic drugs (DMARDs) like methotrexate/sulfasalazine/leflunomide, biologic agents like TNF inhibitors (etanercept, adalimumab, infliximab, golimumab, certolizumab pegol) and IL-1 inhibitors (anakinra, canakinumab), IL-6 inhibitor (tocilizumab), T-cell costimulation inhibitor (abatacept), corticosteroids (prednisone, prednisolone, methylprednisolone), intra-articular corticosteroid injections, physical/occupational therapy, exercise, assistive devices, and surgery (rarely).
• NSAIDs often serve as first-line drugs for pain and inflammation relief.
• DMARDs suppress the underlying disease and prevent joint damage.
• Biologic agents treat patients who don't respond to DMARDs.
• Corticosteroids are strong anti-inflammatory agents for acute flares.
• Physical and occupational therapy are important for keeping joint function up and preventing disability.
• Regular eye exams are crucial for JIA patients, especially with oligoarthritis, to check for uveitis.

Prognosis of JIA

• JIA prognosis varies by subtype and disease severity.
• Early diagnosis and aggressive treatment help many children with JIA achieve remission and live normal lives.
• Some patients still have chronic pain, joint damage, and disability despite treatment.
• Poorer prognosis factors include systemic arthritis, polyarthritis (RF positive), early onset, hip involvement, and delayed diagnosis/treatment.
• Untreated uveitis can lead to blindness.
• Growth disturbances can result from chronic inflammation and corticosteroid use.
• JIA patients face a higher risk of osteoporosis, cardiovascular disease, and other long-term issues.