The imprecision of dual bone marrow/leukocytes SPECT/CT imaging without bone scan in evaluating infected pelvic pressure ulcers

Objectives When pelvic bones uptake is noted in In-111 leukocytes scan (WBCS), bone marrow scan (BMS) is inevitably needed to distinguish between true osteomyelitis (OM) uptake from non specific uptake due to bone marrow hyperplasia (BMH). In routine dual isotope (DI) SPECT/CT protocol, BMS/WBCS (step 2) is performed the second day following bone scan (BS) /WBCS (step 1) completion. We evaluated the utility of step 2 DI SPECT/CT alone in patients with pressure ulcers in an attempt to shorten study duration and reduce radiation exposure.

Methods DI SPECT/CT step 1 and 2 images of consecutive 29 pelvic ulcer patients were examined. Blinded evaluations of step 2 images were initially performed by 2 observers followed by evaluations of both step 1 and 2 images. Diagnosis was categorized as OM with soft tissue infection (STI), STI only, BMH, other/no pathology, and diagnostic accuracy and confidence of DI step 2 SPECT/CT only were compared to DI step 1 and 2 SPECT/CT. Bone lesions were classified as OM when BS showed similar/greater uptake and BMS showed less uptake than WBCS, and classified as BMH when BS showed less uptake and BMS showed similar/greater uptake than WBCS.

Results DI Step 1 and 2 SPECT/CT confirmed 14 OM with STI, 4 STI only, 9 BMH, 2 no/other pathology. DI step 2 SPECT/CT correctly diagnosed all BMH but underdiagnosed OM (10/14) and overdiagnosed STI only (8/4) with a Lambda value of 0.71. In these 4 cases, STI were contiguous to bone without clear bony uptake in WBCS or BMS but with definite abnormal uptake in BS. The overall confidence in diagnosis was significantly higher in DI step 1 and 2 SPECT/CT than step 2 SPECT/CT alone (p < 0.001).

Conclusions In our study group, both DI step 1 and 2 SPECT/CT images were needed to accurately and confidently distinguish between OM with STI from STI only in patients with infected pelvic pressure ulcers. Step 2 SPECT/CT alone without BS underdiagnosed patients with OM, which could have detrimentally affected their management.