Ga-67-citrate and Tc-99(m)-MDP for estimating the severity of vertebral osteomyelitis

The aim of this study was to evaluate the roles of Ga-67-citrate and Tc-99( m)-methylene diphosphonate (Tc-99(m)-MDP) planar and single photon emission tomographic (SPET) imaging in patients with vertebral osteomyelitis. Thirt y patients (22 females, 8 males) aged 62.7 +/- 16.4 years (mean +/- s) were enrolled prospectively between May 1995 and May 1998. The patients had bee n on antibiotics for 7 +/- 4 weeks prior to the study. Histology was availa ble for all but nine patients with mild infections, who were evaluated by a combination of magnetic resonance imaging (MRI), clinical and laboratory t ests. Ga-67-citrate (185 MBq) and three-phase bone (555 MBq Tc-99(m)-MDP) p lanar and SPET imaging were performed in all patients, together with MRI as a comparison. In total, 67 infectious foci were detected. Based on histolo gy, there were four cases of severe, 13 cases of moderate and four cases of mild osteomyelitis; nine mild infections were also classified by the combi nation of MRI, clinical and laboratory results. Combined MRI and Ga-67-citr ate SPET correctly classified all patients; MRI detected all 67 infectious foci, whereas 67Ga-citrate SPET identified 54 only. False-negative results were seen with all other modalities, especially in cases of mild and modera te infection. 67Ga-citrate SPET identified unsuspected cases of endocarditi s (n = 2), paravertebral abscess (n = 1), subaxillary soft tissue abscess ( n = 1) and rib osteomyelitis (n = 1). For 67Ga-citrate SPET, the target-to- background ratio was 2.24 +/- 0.31, 1.76 +/- 0.07 and 1.30 +/- 0.18 for sev ere, moderate and mild osteomyelitis, respectively. Significant differences were noted between severe and moderate infection (P = 0.0051) and between severe and mild infection (P < 0.0001); that between moderate and mild infe ction was non-significant. For Tc-99(m)-MDP planar and SPET imaging, and fo r planar Ga-67-citrate imaging, there was no correlation with severity. We conclude that 67Ga-citrate SP:ET is able to identify vertebral osteomyeliti s and detect additional sites of infection. It can also aid in determining the severity of infection and, potentially, the response to therapy. ((C) 2 000 Lippincott Williams & Wilkins).