What is the initial approach for a 16-year-old female presenting with polyarticular (multiple joint) pain, including recommended laboratory tests and potential treatments?

Initial Approach to a 16-Year-Old Female with Polyarticular Joint Pain

The initial approach for a 16-year-old female with polyarticular joint pain should include laboratory testing for juvenile idiopathic arthritis (JIA), with methotrexate as first-line treatment for those diagnosed with polyarticular JIA.

Diagnostic Evaluation

Key Clinical Assessment

• Determine disease chronology: acute vs. chronic pain
• Assess for inflammatory features:
  • Morning stiffness (>1 hour suggests inflammatory arthritis)
  • Joint warmth, swelling, and tenderness
  • Distribution pattern (symmetric vs. asymmetric)
  • Extra-articular manifestations (rash, fever, weight loss, fatigue)

Essential Laboratory Tests

1. Complete blood count (CBC)
2. Inflammatory markers:
   • Erythrocyte sedimentation rate (ESR)
   • C-reactive protein (CRP)
3. Autoimmune markers:
   • Rheumatoid factor (RF)
   • Anti-cyclic citrullinated peptide (anti-CCP) antibodies
   • Antinuclear antibody (ANA)
4. Metabolic panel
5. Urinalysis

Imaging Studies

• Plain radiographs of affected joints (hands/wrists, feet)
• Consider MRI for early detection of erosions or if diagnosis is uncertain
• Ultrasound to detect synovitis in doubtful cases (more sensitive than clinical examination)

Treatment Algorithm for Polyarticular JIA

Initial Therapy

1. DMARD therapy is strongly recommended over NSAID monotherapy 1

   • Methotrexate is the preferred first-line DMARD (conditionally recommended over leflunomide or sulfasalazine) 1
   • Subcutaneous methotrexate is conditionally recommended over oral administration 1

2. For patients without risk factors (negative RF, negative anti-CCP, no joint damage):

   • Initial therapy with methotrexate is conditionally recommended over biologic therapy 1

3. For patients with risk factors (positive RF, positive anti-CCP, joint damage):

   • While methotrexate is still conditionally recommended as initial therapy, biologic therapy may be considered earlier, especially with:
     • High-risk joint involvement (cervical spine, wrist, hip)
     • High disease activity
     • High risk of disabling joint damage 1

Adjunctive Therapies

1. NSAIDs as adjunct therapy (not as monotherapy) 1
2. Intra-articular glucocorticoid injections 1
   • Triamcinolone hexacetonide is strongly preferred over triamcinolone acetonide 1
3. Short-term oral glucocorticoids (<3 months) during initiation of therapy for moderate/high disease activity 1
   • Avoid in patients with low disease activity 1
   • Strongly recommended against chronic low-dose glucocorticoids 1
4. Physical and occupational therapy for patients with functional limitations 1

Subsequent Therapy (if inadequate response)

1. For patients on methotrexate with inadequate response after 3 months:

   • Adding a biologic (TNF inhibitor such as etanercept, adalimumab) is conditionally recommended over switching to another DMARD 1
   • Combination therapy with methotrexate and a biologic is conditionally recommended over biologic monotherapy 1
   • For infliximab specifically, combination with methotrexate is strongly recommended 1

2. Available biologics with evidence in polyarticular JIA:

   • TNF inhibitors (etanercept, adalimumab, golimumab) 2, 3
   • Non-TNF biologics (abatacept, tocilizumab) 1

Monitoring and Follow-up

• Regular assessment of disease activity using clinical juvenile disease activity score (cJADAS-10)
• Low disease activity defined as cJADAS-10 ≤2.5 and ≥1 active joint
• Moderate/high disease activity defined as cJADAS-10 >2.5 1
• Follow-up every 3 months until disease control achieved
• Radiographic assessment annually to monitor for joint damage

Important Considerations and Pitfalls

1. Don't delay treatment - Early aggressive therapy is critical to prevent permanent joint damage and improve long-term outcomes 1

2. Don't rely solely on laboratory tests - Many classic rheumatologic laboratory tests are nonspecific 4

3. Don't miss differential diagnoses - Consider other causes of polyarticular pain:

   • Viral infections (acute, self-limited)
   • Crystal-induced arthritis
   • Serum sickness reactions
   • Osteoarthritis (though less common in adolescents)
   • Other rheumatologic conditions 4, 5

4. Don't undertreat - The goal is to achieve low disease activity or remission to prevent long-term joint damage 1

5. Don't overlook functional assessment - Physical and occupational therapy are important components of comprehensive care 1