Photopenic defects in marrow-containing skeleton on indium-111 leucocyte scintigraphy: prevalence at sites suspected of osteomyelitis and as an incidental finding.

The skeletal distribution of red marrow-containing sites with a decreased uptake of indium-111-labelled leucocytes was examined as part of a retrospective review of 128 consecutive scans in 113 patients. The prevalence of photopenic defects was determined for sites of suspected osteomyelitis and for other skeletal locations included as part of limited or total-body surveys. Of 52 sites suspected of osteomyelitis based upon radiological and clinical data, 21 (40%) demonstrated a decreased leucocyte uptake. The prevalence of photopenia ranged from 79% (11/14) in the spine and 63% (5/8) in the pelvis to 25% (4/16) in the proximal femur and 0% elsewhere in the extremities (0/9) and in the skull (0/3). Fourteen of these 21 defects (67%) were due to active (n = 9) or healed (n = 5) osteomyelitis/discitis. All sites of active osteomyelitis showed destructive changes on correlative radiographs and were associated with infectious processes of more than 1 months duration. Thirty-seven photopenic defects were observed as incidental findings. The prevalence of photopenia as an incidental finding ranged from 0% in the skull, neck and chest to 3%-4% in the thoracolumbar spine and pelvis and 14% in the femoral heads, the latter reflecting primarily bilateral loss of femoral head marrow. No incidentally found photopenic defect reflected active osteomyelitis. At sites in the spine and pelvis with radiologic evidence of bone destruction suggestive of osteomyelitis, an absence of normal red marrow uptake of labelled leucocytes often reflects a variant presentation for active chronic infection. In contrast, incidental photopenia is uncommon at all skeletal sites except the femoral heads, and should not raise concern over unsuspected active osteomyelitis.