Reasons for failure to classify 11 patients out of a cohort of 235 with juvenile idiopathic arthritis into a discrete (possible) category and further classifying as undifferentiated arthritis, as per the ILAR classification system (Edmonton, 2001).
| Possible Category | No. Patients | Cause of Exclusion/Second Category | No. Patients | Remarks |
|---|---|---|---|---|
| OLA-P | 4 | RF+ | 3 | All females |
| RF+, HLA-B27+ | 1 | Male, onset age ≥ 6 yrs | ||
| OLA-E | 5 | RF+ | 3 | All females |
| RF+, HLA-B27+ | 2 | Male | ||
| Systemic arthritis | 1 | RF+ | 1 | Male |
| Psoriatic arthritis | 1 | HLA-B27+, enthesitis-related arthritis | 1 | Male |
OLA: oligoarthritis; P: persistent; E: extended; ILAR: Internal League of Associations for Rheumatology.