The criteria usually accepted for the diagnosis of osteomyelitis by combined scanning states that the gallium scan must show an increased target-to-background ratio over that seen on the bone scintigraphy indicating the presence of infection. A normal gallium scan implies inactive disease. Lisbona and Rosenthal studied forty consecutive patients referred for possible inflammatory disease with both bone and gallium scans. Sixteen patients showed some form of active osteomyelitis, including chronic active osteomyelitis, all of whom demonstrated both positive bone and gallium scans. The authors state, "The Tc-99m-MDP images were in general more intensely positive than the gallium images." Three patients had disease classified as inactive osteomyelitis, all of whom had radiographs similar to the patient described above, and negative gallium images. Hoffer takes mild exception to the last statement, stating, "Chronic osteomyelitis may rarely take up gallium." Alazraki studied patients with chronic osteomyelitis with bone scans, correlating the ratio of the uptake in the abnormal extremity over those in the normal extremity to the clinical course of the patient while on antibiotic therapy. She concluded that this ratio fell as the patient underwent a positive clinical response.
Other articles have not focused on chronic osteomyelitis, but on the use of combined imaging in osteomyelitis in general. Rosenthal studied patients with previously inserted orthopedic devices and concluded that congruency in uptake between the two studies was important in interpretation. Congruent uptake between the two studies with no focally increased gallium uptake suggested the absence of osteomyelitis. Non congruency or marked focally increased gallium uptake suggested osteomyelitis, cellulitis, or nonseptic synovitis. Graham induced osteomyelitis in the tibias of rabbits and followed the animals with gallium scans while under treatment. All 25 rabbits with negative gallium scans at the end of six weeks of antibiotics were culture-negative. Eighteen rabbits with positive gallium scans at the end of six weeks were nearly equally divided between positive and negative culture groups. Rosenthal's study does support the contention that increased gallium uptake in the same distribution as increased bone uptake is necessary for the interpretation of osteomyelitis. Graham's data do support the statement that a negative gallium scan implies inactive disease.
In the patient above, bone biopsy was performed prior to surgery, and all debrided fragments were submitted for culture. All cultures were negative at the time of discharge ten days following surgery. At least in this instance, our criteria performed quite well.
2) Hoffer P. Gallium and infection. J Nucl Med 1980; 21:484.
3) Rosenthal L. 99m-Tc-PP and Ga-67 imaging following insertion of orthopedic devices. Radiology 1979; 133:717.
4) Graham GD. Predicting the cure of osteomyelitis under treatment: concise communication. J Nucl Med 1983; 24:110.
5) Alazraki NP. The role of gallium and bone scanning in monitoring response to therapy in chronic osteomyelitis. J Nucl Med (abstract) 1978:19:696.
J. Anthony Parker, MD PhD, firstname.lastname@example.org