Tc-99m-interleukin-8 for imaging acute osteomyelitis

Early and accurate diagnosis of osteomyelitis remains a clinical problem. A cute osteomyelitis often occurs in infants and most often is located in the long bones. Radiologic images show changes only in advanced stages of dise ase. Scintigraphic imaging with Tc-99m-methylene diphosphonate (MDP), or bo ne scanning, is much more sensitive in detecting acute osteomyelitis but la cks specificity. We evaluated the performance of Tc-99m-interleukin-8 (IL-8 ) in an experimental model of acute osteomyelitis. Methods: Acute pyogenic osteomyelitis was induced in 10 rabbits by inserting sodium morrhuate and S taphylococcus aureus into the medullary cavity of the right femur. The cavi ty was closed with liquid cement. A sham operation was performed on the lef t femur. Routine radiographs were obtained just before scintigraphy. Ten da ys after surgery, the rabbits were divided into 2 groups of 5 animals, rece ived an injection of either 18.5 MBq In-111-granulocytes or 18.5 MBq Ga-67- citrate, and were imaged both 24 h after injection and 48 h after injection . On day 12, the rabbits received either 18.5 MBq Tc-99m-MDP or 18.5 MBq Tc -99m-IL-8, and serial images were acquired at 0, 1, 2, 4, 8, 12, and 24 h a fter injection. Uptake in the infected femur was determined by drawing regi ons of interest. Ratios of infected femur (target) to sham-operated femur ( background) (T/Bs) were calculated. After the final images were obtained, t he rabbits were killed and the right femur was dissected and analyzed for m icrobiologic and histopathologic evidence of osteomyelitis. Results: Acute osteomyelitis developed in 8 of 10 rabbits. All imaging agents correctly de tected the acute osteomyelitis in these animals. The extent of infection wa s optimally visualized with Ga-67-citrate and delayed bone scanning, wherea s diaphyseal photopenia was noted with both Tc-99m-IL-8 and In-111-granuloc ytes. In 1 rabbit with osteomyelitis, imaging results were falsely negative with In-111-granulocytes and falsely positive with Tc-99m-MDP. Quantitativ e analysis of the images revealed that the uptake in the infected region wa s highest with Ga-67-citrate (4.9 +/-0.8 percentage injected dose [%ID]) an d Tc-99m-MDP (4.7 +/-0.7 %ID), whereas the uptake in the infected area was significantly lower with Tc-99m-IL-8 (2.2 +/-0.2 %ID) and In-111-granulocyt es (0.8 +/-0.2 %ID) (P<0.0042). In contrast, the T/Bs were significantly hi gher for Tc-99m-IL-8 (T/B, 6.2<plus/minus>0.3 at 4 h after injection) than for Ga-67-citrate, Tc-99m-MDP, and In-111-granulocytes, which had ratios of 1.5 +/-0.4, 1.9 +/-0.2, and 1.4 +/-0.1, respectively (P<0.0001). Radiograp hy correctly revealed acute osteomyelitis in only 2 of 8 rabbits. Conclusio n: In this rabbit model of osteomyelitis, Tc-99m-IL-8 clearly revealed the osteomyelitic lesion. Although the absolute uptake in the osteomyelitic are a was significantly lower than that obtained with Tc-99m-MDP and Ga-67-citr ate, the T/Bs were significantly higher for Tc-99m-IL-8 because of fast bac kground clearance. The ease of preparation, good image quality, and lower r adiation burden suggest that Tc-99m-IL-8 may be a suitable imaging agent fo r the scintigraphic evaluation of acute osteomyelitis.