Pyogenic Sacroiliitis in Older Adults Presenting With Massive Retroperitoneal Abscess: A Case Report.

Pyogenic sacroiliitis (PSI) is an uncommon form of septic arthritis and is frequently diagnosed late in older adults because initial symptoms are nonspecific and imaging findings may be misattributed to other sources of infection. We report two older patients with PSI complicated by massive retroperitoneal and gluteal abscesses, highlighting the importance of early recognition and, when indicated, timely surgical source control. Case 1 was an 83-year-old woman in whom a conspicuous retroperitoneal abscess and abnormal urinalysis led to suspicion of an intra-abdominal or urinary tract source, delaying recognition of PSI. Despite antibiotics, she deteriorated with organ dysfunction; re-evaluation of the initial magnetic resonance imaging MRI identified the sacroiliac joint as the primary focus, and staged surgical drainage procedures were required, followed by a prolonged recovery. Case 2 was a 70-year-old woman who presented in septic shock after failing outpatient treatment for presumed lumbar spine disease. Based on the diagnostic pitfalls in Case 1, PSI was immediately suspected; emergency drainage of both retroperitoneal and gluteal collections was performed on the day of presentation, which was followed by rapid stabilization and recovery. These cases emphasize that, in older patients with low back or gluteal pain, the concurrent presence of retroperitoneal and gluteal abscesses should prompt careful evaluation of the sacroiliac joint. These observations suggest that early diagnosis and timely assessment for surgical source control may contribute to favorable outcomes in severe cases.