Diagnosis and Management of Undifferentiated Peripheral Inflammatory Arthritis

Introduction to Inflammatory Arthritis

The American College of Rheumatology suggests that undifferentiated peripheral inflammatory arthritis (UPIA) requires urgent evaluation to exclude infectious causes and establish a specific diagnosis, given the presentation of acute-onset bilateral polyarthritis with markedly elevated inflammatory markers 1

Elevated CRP (78 mg/L) and ESR (29 mm/h) are indicative of active systemic inflammation, ruling out non-inflammatory causes like osteoarthritis, with the European League Against Rheumatism (EULAR) recommending the use of CRP as a reliable marker of inflammation 1, 2
A negative rheumatoid factor (14.1) and anti-CCP IgG (8) make classic seropositive RA less likely but do not exclude it, as seronegative RA accounts for 20-30% of cases, according to the American College of Rheumatology 2
A negative ANA makes systemic lupus erythematosus and other connective tissue diseases less likely, as stated by the European League Against Rheumatism (EULAR) 1, 2

The American College of Rheumatology recommends arthrocentesis of at least one swollen joint for cell count, Gram stain, culture, and crystal analysis to exclude septic arthritis and post-streptococcal reactive arthritis before assuming autoimmune disease 1, 5, 6
Blood cultures, throat culture, or rapid strep test should be performed if febrile or if there is an elevated ASO, as suggested by the Infectious Diseases Society of America 1

Post-streptococcal reactive arthritis is the most likely diagnosis given the acute 2-day onset, elevated ASO, and migratory polyarthritis pattern, according to the American College of Rheumatology 1
Seronegative rheumatoid arthritis is possible given symmetric small joint involvement, but the acute onset is atypical, as noted by the European League Against Rheumatism (EULAR) 2

The American College of Rheumatology recommends holding any potential immunosuppressive therapy until infection is excluded, and using prednisone (0.5-1 mg/kg/day) for severe inflammatory arthritis, with the European League Against Rheumatism (EULAR) suggesting the use of NSAIDs at therapeutic doses for additional pain control 4, 5
Methotrexate (15 mg weekly) should be started as first-line DMARD if infection is excluded and RA is suspected, with folic acid (1 mg daily) to reduce methotrexate toxicity, as recommended by the American College of Rheumatology 2, 4, 5

The American College of Rheumatology suggests referring immediately to rheumatology given definite synovitis with severe functional impairment, grade 3-4 disease severity, or diagnostic uncertainty between reactive arthritis and early RA 1, 4, 5, 6
Serial rheumatologic examinations and inflammatory markers should be monitored every 4-6 weeks once treatment is initiated, as recommended by the European League Against Rheumatism (EULAR) 4, 5, 6