Pubic symphysitis of enthesitis related arthritis mimicking urinary tract infection in a young boy

Enthesitis related arthritis (ERA) is a specific type of juvenile idiopathic arthritis (JIA) and ERA typically begins with enthesitis and peripheral arthritis in the lower extremities, progressing later in the disease to sacroiliitis and spinal involvement. The condition has a strong relationship with the HLA-B27 and primarily affects boys between the ages of 13 and 16 years. We describe an unusual presentation of ERA in a young boy with pubic pain and fever, describing its quintessential magnetic resonance imaging (MRI) findings. A child presented to the paediatric outpatient department with fever, insidious onset pubic pain and tenderness with associated leukocytosis and elevated inflammatory markers. MRI of the pelvis revealed bilateral symmetrical bone marrow edema involving the pubic symphysis and inferior pubic rami with para symphyseal edema involving bilateral obturator externus muscle and bilateral adductor longus muscle insertions suggestive of enthesitis of the pubic symphysis. MRI also showed sacroiliitis and enthesitis at other sites. HLA-B27 was positive. The patient responded well to a short course of steroids and maintained remission with tumour necrosis factor alpha inhibitors.