AB139. SOH24AB_118. Sacroiliac osteomyelitis mimicking appendicitis: a case report and literature review

Background: The most common serious cause of lower right abdominal pain in children that requires urgent evaluation and management is appendicitis and its related complications (e.g., perforation). This is frequently accompanied by fever and other systemic signs of inflammation. Our case presented with vague right hip/right lower abdominal pain, that was not convincing for appendicitis, however, the diagnostic workup led to the need to exclude appendicitis by laparoscopy, and the final diagnosis was sacroiliac osteomyelitis and septic arthritis.

Case Description: A 14-year-old boy presented with right hip/lower abdomen pain and difficulty weight bearing on the right side, fever for one day. He had negative hip X-rays and continued to spike his temperature once per day for 2 days as an inpatient. Blood cultures were initially positive for salmonella. He then complained of a vague lower right abdominal pain, he was not clinically tender. The orthopedics opinion was that the hip joint was not involved so the general surgeon took over, after another day of spiking temperatures and complaining of pain, a computed tomography (CT) scan of his abdomen was initially reported as normal, then there was a suspicion of acute appendicitis. Subsequently, we proceeded with a diagnostic laparoscopy. It was not convincing for appendicitis; however, laparoscopic appendectomy was carried out. On the first day post-operative he improved dramatically and started to bear weight. No further temperature spikes. A magnetic resonance imaging (MRI) pelvis was also done and it showed a small amount of fluid in the sacroiliac joint and around the psoas muscle. He was then discharged. Represented again with right side pain and temperature spikes, blood results were not very impressive. He proceeded to have a second MRI Pelvis which showed right sacroiliac osteomyelitis, septic arthritis, and capsulitis, with psoas and iliacus abscesses. He settled after a period of intravenous antibiotics and supportive treatment. The histology report of the appendectomy showed lymphoid hyperplasia only.

Conclusions: Due to the lack of consistent pathognomonic signs and symptoms of sacroiliitis, there is often a delay in diagnosis. Clinicians should always keep pyogenic sacroiliitis in mind when a patient presents with abdominal pain accompanied by pelvic or lower extremity musculoskeletal pain. Although an unusual diagnosis in an otherwise healthy child, sacroiliitis should be considered when a child presents with a chief complaint of abdominal pain. MRI of the hip and pelvis with and without contrast is the preferred imaging.

Keywords: Sacroiliac osteomyelitis; acute appendicitis; septic arthritis; right lower abdominal pain; psoas abscess