Sciatica caused by pyomyositis of the piriformis muscle.

Because the sciatic nerve leaves the pelvis through the greater sciatic notch underneath the piriformis muscle, any pathology of the piriformis muscle could result in entrapment of the sciatic nerve; this is widely known as piriformis muscle syndrome. Pyomyositis of the piriformis muscle may be a cause of piriformis muscle syndrome. Piriformis muscle syndrome caused by pyomyositis of the piriformis muscle in pediatric patients is rare. This article describes a case of sciatica caused by pyomyositis of the piriformis muscle in a pediatric patient. A 6-year-old boy presented with right buttock and thigh pain following a mild fever and sore throat. The pain worsened, and he became unable to walk. On admission, his temperature was 38.4°C. He reported severe right-sided buttock and lateral thigh pain. Positive Freiberg sign was observed. Laboratory examination revealed elevated white blood cell count and C-reactive protein level. T2-weighted magnetic resonance images of the pelvis revealed high-intensity changes of the piriformis muscle and iliosacral joint. Thus, piriformis syndrome caused by pyomyositis of the piriformis muscle was diagnosed. Oral antibiotics (10 mg/kg per day of cefdinir) were administered. Pain gradually decreased, and the patient was able to walk. Final follow-up examination at 6 months after symptom onset revealed no sciatic pain. Follow-up magnetic resonance imaging revealed normalized intensities of the piriformis muscle. The endopelvic fascia provides a route for infection from the pelvis to the piriformis. The pyomyositis of the piriformis muscle in the current case may have occurred secondary to the pyoarthritis of the sacroiliac joint. Endopelvic infections involving the piriformis muscle may mimic hip diseases in pediatric patients.