Genuine ankylosing spondylitis in children: a case-control study of patients with early definite disease according to adult onset criteria.

OBJECTIVE: To describe a group of children with spinal and sacroiliac (SI) joint involvement since the initial year of disease, who fulfilled current adult onset ankylosing spondylitis (AS) diagnostic criteria within 3 years of onset.
METHODS: We conducted a case-control study of 44 patients with juvenile onset definite AS. 14 cases (Group A) and 30 controls (Group B) were studied; groups were matched by age at onset (age < or = 16 years), duration of disease at the time of admission to our clinic (< or = 1 year), diagnostic criteria (New York criteria), and period of observation. We compare demographic characteristics, as well as peripheral joint disease 6 and 12 months after onset, and analyze Group A at time of diagnosis. In contrast to Group A, patients in Group B had a syndrome of peripheral arthritis and enthesitis (SEA syndrome), but no axial symptoms or definite diagnosis of AS in the first 5 years of disease.
RESULTS: Patients in Group A were HLA-B27 positive boys with peripheral arthritis and enthesitis who differed from those in Group B in the frequency of pauciarthritis and polyarthritis at one year of disease (0 vs 36.7% and 100.0 vs 63.3%; p = 0.008) and age at diagnosis (9.03 +/- 1.13 vs 16.5 +/- 3.3 years; p > 0.0001). Six patients in Group A had lumbar pain and 3 SI joint pain 6 months after onset; at the end of the first year, the number increased to 10 and 6 patients, respectively. At time of diagnosis (2.36 +/- 0.72 yrs after onset), all patients in Group A had radiographic sacroiliitis and spinal, SI, and/or costosternal pain, 11 reduced anterior spinal flexion, and 6 reduced chest expansion.
CONCLUSION: There is a less common subgroup of adult-like juvenile onset AS who develop clinical and radiographic evidence of disease affecting the axial skeleton earlier than children progressing from SEA syndrome to AS 5 to 10 years after onset.