99mTc-nanocolloid scintigraphy for assessing osteomyelitis in diabetic neuropathic feet

Distinguishing osteomyelitis from neuropathic osteoarthropathy in diabetic feet is a common and difficult clinical problem with no highly accurate discriminatory investigation. This study assesses the novel use of marrow scintigraphy and compares it with magnetic resonance imaging (MRI) for the diagnosis of osteomyelitis in neuropathic osteoarthropathic diabetic feet. Nine diabetic patients with chronic foot ulcers were prospectively assessed independently using 99mTc-nanocolloid scintigraphy and MRI. Those patients showing features of osteomyelitis underwent percutaneous bone biopsy or surgical ray excision for histological confirmation. Other patients were followed up clinically for a minimum of 6 months to exclude osteomyelitis. Marrow scintigraphy, in agreement with MRI, demonstrated all four cases of biopsy proven osteomyelitis and excluded three cases with neuropathic osteoarthropathy alone. One case of suspected osteomyelitis of the ankle on marrow scintigraphy, but not MRI, was not confirmed clinically. One case of suspected osteomyelitis on both imaging modalities was shown on biopsy to demonstrate changes of avascular necrosis but not osteomyelitis. In this study 99mTc-nanocolloid scintigraphy shows a sensitivity of 100% and specificity of 60%. An important false positive result is seen with avascular necrosis, both on marrow scintigraphy and on MRI. Although larger studies are needed to evaluate this technique, 99mTc-nanocolloid marrow scintigraphy may be an alternative to MRI for assessing diabetic feet for osteomyelitis.