Periostitis and Localized Myositis in Polyarteritis Nodosa

A 20-year-old man with known polyarteritis nodosa was referred for bone scintigraphy to investigate bilateral knee and lower leg pain, which worsened with reduction in steroid dose. Plain radiographs of the hips and lower extremities were normal. Blood pool images showed increased vascularity in the anterolateral muscle compartments of the lower legs, suggestive of localized myositis, which was confirmed with subsequent magnetic resonance imaging and muscle biopsy. Delayed bone scans showed widespread, patchy increase in subperiosteal tracer activity with no evidence of avascular necrosis. Bone scintigraphy should be considered in patients with polyarteritis nodosa who report persistent lower extremity pain.