Diagnostic utility of T1-weighted MRI characteristics in evaluation of osteomyelitis of the foot.

OBJECTIVE: The purpose of this study was to evaluate the diagnostic utility of specific characteristics on T1-weighted MR images in the diagnosis of pedal osteomyelitis. MATERIALS AND METHODS: The study included all adult patients who underwent MRI of the foot for evaluation of suspected osteomyelitis over an 11-month period. Images were retrospectively reviewed for specific criteria on T1-weighted images, including signal intensity of affected bone marrow (normal or decreased), distribution of abnormal signal intensity (subcortical or medullary), and pattern of involvement (hazy reticulated or confluent). The presence of osteomyelitis was presumed if the surgical pathologic result was positive or if there was lack of clinical improvement despite conservative management. Rapid clinical improvement with conservative management was considered an indication that osteomyelitis was not present. RESULTS: Images from 74 examinations were evaluated. In 20 cases, osteomyelitis was considered present, and in 54 it was presumed absent. In 19 of the 20 cases (95%) in which osteomyelitis was considered present, marrow T1 signal intensity was decreased, in a medullary distribution, and in a confluent pattern in all cases. In 30 of the 54 cases (56%) in which osteomyelitis was presumed absent, T1 signal intensity was decreased, but only five cases (9%) had a medullary distribution and confluent pattern. Twenty-three cases (43%) had a hazy reticulated pattern, and two cases (4%) had only subcortical distribution. None of the cases with a subcortical distribution or hazy reticulated pattern of abnormal signal intensity had positive results for osteomyelitis. Confluent decreased T1 marrow signal intensity in a medullary distribution was 95% sensitive in the prediction of osteomyelitis with a specificity of 91%, negative predictive value of 98%, and positive predictive value of 79%. CONCLUSION: Findings on T1-weighted MR images, specifically a confluent pattern of decreased T1 marrow signal intensity in a medullary distribution, correlate highly with the presence of pedal osteomyelitis.

Serum-starvation-induced changes in protein synthesis and morphology of Borrelia burgdorferi.

It has been demonstrated previously that motile Borrelia burgdorferi cells transform into non-motile cyst-forms when incubated for several weeks in BSKII (a complex medium) lacking rabbit serum. B. burgdorferi cells cannot synthesize fatty acids de novo and serum is thought to provide a source of fatty acids and lipids. When B. burgdorferi cells were serum-starved in defined RPMI medium, -90% of the cells formed spherical cysts within 48 h. Cyst formation was inhibited by tetracycline. Cyst opening and recovery of vegetative cells was rapidly induced by the addition of either BSKII or rabbit serum. The percentage of viable cells recovered from cysts ranged from 2.9% to 52-5%. Viability was inversely proportional to cyst age. Protein synthesis by B. burgdorferi during serum starvation was examined by labelling cells with Tran35S-Label and analysing the labelled proteins by two-dimensional gel electrophoresis and fluorography. The synthesis of over 20 proteins was induced during serum starvation. Western blots of proteins from vegetative cells and cysts probed with sera from either B. burgdorferi-infected humans or monkeys revealed that several cyst proteins were antigenic. These data suggest that cells of B. burgdorferi, although possessing a small genome and extremely limited biosynthetic capabilities, rapidly respond to conditions of serum starvation by inducing changes in protein synthesis and cell morphology. This study may help explain how cells of B. burgdorferi can survive periods of nutrient deprivation in different hosts and host tissues.