Comparison of Tc-99m methylene diphosphonate, Tc-99m human immune globulin, and Tc-99m-labeled white blood cell scintigraphy in the diabetic foot.

Purpose: The aims of this prospective study were to evaluate the contribution of Tc-99m methylene diphosphonate (MDP), Tc-99m human immune globulin (HIG), and Tc-99m white blood cell (WBC) to the diagnosis of osteomyelitis in the diabetic foot and to evaluate the surgical or medical therapy with Tc-99m HIG and Tc-99m WBC scans.

Methods: Twenty patients (15 men, 5 women) with suspected pedal osteomyelitis were included in the study. All patients had type II diabetics. Three- and four-phase bone scintigraphy (3P-MDP, 4P-MDP), early (e) and late (l) HIG, and WBC scans were completed within 1 week in all patients. The lesion-to-background ratios were calculated for early and late images of the feet for all scans and named as the indices. Eight weeks after the end of medical or surgical therapy, Tc-99m HIG and Tc-99m WBC scans were repeated in 10 patients. The difference in indices between 3P-MDP and 4P-MDP for osteomyelitis and indices for osteomyelitis, cellulitis, and inflammation in Tc-99m HIG and Tc-99m WBC in early and late scans were tested for significance.

Results: In 20 patients, 53 lesions were investigated. Among these 53 lesions were 25 sites of proved osteomyelitis, 6 sites of cellulitis, and 22 sites of inflammation confirmed by radiography, microbiologic culture, and clinical evaluation. 4P-MDP was more specific than 3P-MDP for detecting osteomyelitis (50% and 67%, respectively). There was also a significant difference between the mean indices of 3P-MDP and 4P-MDP (P < 0.000). The index values were increased in 4P-MDP scans. There was no significant difference between the indices of early and late Tc-99m HIG scans for inflammation, cellulitis, and osteomyelitis. Early and late Tc-99m WBC scans did not show a significant difference in differentiating osteomyelitis. However, Tc-99m WBC scans could differentiate aseptic inflammation from infection (P < 0.031) in early and late scans. There was a significant difference of index values between pre- and post-treatment Tc-99m HIG and Tc-99m WBC scans. The best combination of scans for detecting osteomyelitis was 4P-MDP with WBC scans, with an accuracy rate of 92%.

Conclusions: These results show that four-phase bone scintigraphy with early Tc-99m WBC scanning is preferred for detecting osteomyelitis of the diabetic foot. To evaluate the response to therapy, Tc-99m WBC scans are the preferred method, but if this is not available, Tc-99m HIG scanning can be used.