The scintigraphy findings of a patient with possible osteomyelitis are discussed below and the history of this patient is illustrated in Figures 9.3 to 9.5 in Chapter 9.
A plain radiograph showed findings compatible with osteomyelitis or neuro-osteoarthropathy of the second and third
metatarsal heads of this female patient. She was referred for a technetium-99m (99Tc) phosphonate scan. Images obtained during the flow phase are shown in the left upper panel of Figure 8.37; during this phase a series of 3-s image acquisitions of the site in question is obtained. They showed increased radionuclide uptake by the tarsometatarsal area of her left foot. A static blood pool image (blood pool phase) obtained 5 min later is shown in the right upper panel. A static delayed image (delayed phase) obtained 3 h later is shown in the left lower panel. All images showed increased uptake in the same areas. A gallium-67 citrate study performed on the same day (right lower panel of Figure 8.37), showed increased radionu-clide uptake at the tarsometatarsal area. Based on the results of bone scintigra-phy the patient was diagnosed as having osteomyelitis in the tarsometatarsal area.
99Tc scintigraphy is useful in cases of questionable osteomyelitis. It has a high sensitivity (over 90%) but a low specificity (33%), particularly in the presence of neuro-osteoarthropathy. Although increased radionuclide uptake during the flow and pool phase is not specific to the diagnosis of osteomyelitis (it may mean soft tissue, bone infection or both), delayed images of the 99Tc scintigraphy showed increased blood flow to the bones only, thus increasing the specificity of the method in the diagnosis of bone infection. Patients with neuro-osteoarthropathy have increased bone blood flow in the absence of osteomyelitis.
Like 99Tc scintigraphy, gallium-67 citrate accumulates in both osteomyelitis and neuro-osteoarthropathy. This is the reason for its low specificity in the diagnosis of osteomyelitis in diabetic patients. Indium-111 white blood cell imaging (111In WBCs) is expensive, time consuming, has poor spatial resolution and does not distinguish soft tissue from bone infection.
Keywords: Scintigraphy; bone scans; diagnosis of osteomyelitis
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