Utility of ^99mTc-labelled antimicrobial peptide ubiquicidin (29-41) in the diagnosis of diabetic foot infection

Detection of osteomyelitis beneath a diabetic foot ulcer is imperative for proper management; however, accurate and noninvasive diagnosis of osteomyelitis remains a challenge. Ubiquicidin 29-41 (UBI 29-41) is a synthetic antimicrobial peptide fragment reported to be highly infection-specific. ^99mTc-UBI 29-41 has recently been reported to be a promising radiotracer for infection imaging. The aim of this prospective study was to evaluate the utility of ^99mTc-UBI 29-41 scintigraphy in diabetic patients with suspected osteomyelitis of the foot.

Included in the study were 65 patients with type 2 diabetes mellitus and foot ulcer and with clinical suspicion of osteomyelitis . Each patient had a three-phase bone scan and a ^99mTc-UBI scan at 30 and 60 min after injection. The scan was considered to be consistent with osteomyelitis when the ^99mTc-UBI 29-41 uptake was concordant with the ^99mTc-MDP uptake. It was considered negative for osteomyelitis if there was no uptake of ^99mTc-UBI 29-41 or if ^99mTc-UBI 29-41 accumulated in an area not concordant with the abnormal uptake of ^99mTc-MDP on the bone scan. In the latter case a diagnosis of soft-tissue infection was made. Bone infection was confirmed by bone biopsy/culture and by clinical and radiological follow-up.

Final analysis was done in 55 patients. Osteomyelitis was confirmed in 37 patients, and 18 patients were free of bone infection. ^99mTc-UBI 29-41 was positive in all 37 patients and with the bone scan as the reference for the bone identified all osteomyelitic foci (68 in total). ^99mTc-UBI 29-41 was negative for osteomyelitis in all 18 patients, and 17 of these patients were diagnosed with soft-tissue infection (^99mTc-UBI 29-41 accumulation without concordant abnormal uptake on bone scintigraphy). The sensitivity, specificity and accuracy of ^99mTc-UBI 29-41 scan in combination with three-phase bone scan for the diagnosis of osteomyelitis in diabetic foot was 100 %. Accuracy for soft-tissue infection was also 100 %. Maximum accumulation of the ^99mTc-UBI 29-41 with maximum target to background activity was observed in the infectious foci at 30 min after injection.

Tc-UBI 29-41 may be a useful agent for the accurate diagnosis of bone infection in diabetic foot because of the high accuracy demonstrated in this pilot study. It was able to differentiate between bone and soft-tissue involvement effectively in combination with a bone scan.