Three cases of pyogenic sacro-iliitis, and factors in the relapse of the disease.

Pyogenic sacro-iliitis (PS) is a rare disease in childhood. Three cases of PS are reported that were difficult to diagnose. Scintigraphy and magnetic resonance imaging (MRI) were useful for diagnosis. One patient suffered from an episode of relapse. Seventeen other cases of PS were reviewed in the literature to investigate the incidence of abnormal imaging findings and various factors in disease relapse. It was found that the incidence of abnormal findings by scintigraphy was significantly higher than that by computed tomography (P = 0.0057). The duration of intravenous antibiotic administration of the relapse group (14.7 +/- 4.7 days) was significantly shorter than that of the non-relapse group (24.3 +/- 10.7 days; P = 0.0376). The statistical analysis suggested that intravenous antibiotic administration is necessary at least for 20 days to prevent a relapse of PS.