Baseline characteristics of included patients with CSA
| All patients (n=600) | Patients developing IA* (n=99) | Patients not developing IA (n=501) | |
| Female | 469 (78) | 71 (72) | 398 (79) |
| Age in years | 44±13 | 47±13 | 43±12 |
| Symptom duration in days | 137 (68–310) | 143 (61–364) | 134 (68–296) |
| ACPA-positive and/or RF-positive | 133 (22) | 56 (57) | 77 (15) |
| ACPA-positive | 79 (13) | 46 (47) | 33 (7) |
| RF-positive | 115 (19) | 52 (53) | 63 (13) |
| CRP increased (≥5 mg/L) | 130 (22) | 34 (34) | 96 (19) |
| ESR increased† | 88 (15) | 27 (27) | 61 (12) |
| HAQ | 0.7±0.5 | 0.8±0.6 | 0.6±0.5 |
| Hand-domain >0 | 402 (67) | 74 (75) | 328 (66) |
| Foot-domain >0 | 175 (29) | 33 (33) | 142 (28) |
| TJC-68 | 5 (2–10) | 5 (2–8) | 5 (2–10) |
| TJC group‡ | |||
| TJC: hands+ feet- | 252 (42) | 41 (41) | 211 (42) |
| TJC: hands- feet+ | 47 (8) | 8 (8) | 39 (8) |
| TJC: hands+ feet+ | 221 (37) | 36 (36) | 185 (37) |
| TJC: hands- feet- | 72 (12) | 12 (12) | 60 (12) |
| Complaints started in joints§ | |||
| Upper extremities | 402 (67) | 61 (62) | 341 (68) |
| Lower extremities | 58 (10) | 12 (12) | 46 (9) |
| Upper and lower extremities | 99 (17) | 19 (19) | 80 (16) |
| MRI inflammation present¶ | |||
| Hand | 208 (35) | 68 (69) | 140 (28) |
| Foot | 76 (13) | 31 (31) | 45 (9) |
Data are n (%), mean±SD or median (IQR).
*88 patients met the definition for RA at moment of IA development, of whom 55 (63%) were autoantibody positive.
†ESR was considered elevated with a reference for age and sex (<50 years: male >15 mm/hour, female >20 mm/hour; >50 years: male >20 mm/hour, female >30 mm/hour).
‡TJC of the hands involved bilaterally: wrist, MCP joints 1–5, PIP joints 2–5 and IP joints of the thumb. TJC of the feet involved bilaterally: the MTP joints 1–5.
§The joints in which symptoms started were registered by the rheumatologist.
¶Subclinical joint inflammation on MRI in hand (MCP joints and wrist) and foot (MTP joints) was dichotomised per feature of inflammation (synovitis, tenosynovitis, osteitis) and per location; if the inflammation score of any feature was higher than present at the same location in <5% of age-matched symptom-free individuals, the joint was considered positive for inflammation.
ACPA, anticitrullinated protein antibody; CRP, C reactive protein; CSA, clinically suspect arthralgia; ESR, erythrocyte sedimentation rate; HAQ, Health Assessment Questionnaire Disability Index; IP, interphalangeal; MCP, metacarpophalangeal; MTP, metatarsophalangeal; PIP, proximal interphalangeal; RA, rheumatoid arthritis; RF, rheumatoid factor; TJC, tender joint count.