Table 2.

Differences Between Down Syndrome-Associated Arthritis and Juvenile Idiopathic Arthritis

Variable	Down Syndrome-Associated Arthritis	Juvenile Idiopathic Arthritis
Prevalence	10/1000	1/1000
Most common presentation	Polyarticular	Oligoarticular
Sex predilection	Equal	Female
Age at onset	6–7 years and 13–20 years	1–3 years and 9–11 years
Normal laboratory tests* at diagnosis	30–45%	5–35%
Imaging damage at diagnosis	Greater than 40%	Less than 25%
Elevated CRP at diagnosis	Less than 20%	Greater than 60%
Elevated ESR at diagnosis	Less than 45%	Greater than 60%
Uveitis (throughout disease course)	Less than 2%	20–30%
Significant Outcome Measure Differences After Treatment n (SD)**
Joints with active arthritis	2.9 (5.6)	0.8 (2.0)
Joints with limited range of motion	3.3 (5.5)	0.8 (2.0)
Clinical Juvenile Arthritis Disease Activity Score 10†	4.4 (4.5)	2.6 (4.5)
Medication intolerance	High	Low
Medication effectiveness	Low	High

Notes: *Normal laboratory tests defined as normal c-reactive protein (CRP), erythrocyte sedimentation rate (ESR), negative antinuclear antibody (ANA), negative rheumatoid factor (RF), and negative human leukocyte antigen B27 (HLA-B27). **Modified from reference.¹³ †Clinical Juvenile Arthritis Disease Activity Score 10; composite disease activity (0–30), sum of the MD-global (completed by provider, 10-point Likert visual analog scale, 0 = clinically inactive disease), Pt-Global (completed by patient or caregiver, 10-point Likert visual analog scale, 0 = very good) and number of joints with active arthritis from physical exam capped at a maximum of 10, ≤ 1.0 = inactive disease.