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BACKGROUND:: Central nervous system injuries after transforaminal epidural steroid injections have been ascribed to occlusion of the blood vessels supplying the spinal cord and brain by the particulate steroid. METHODS:: The authors compared the sizes of the particles of the steroids methylprednisolone acetate, triamcinolone acetonide, dexamethasone sodium phosphate, betamethasone sodium phosphate/betamethasone acetate (both Celestone Soluspan®; Schering-Plough, Kenilworth, NJ, the commercial betamethasone; and betamethasone repository, a betamethasone preparation that can be ordered from a compounding company), and betamethasone sodium phosphate. Both undiluted and diluted samples were examined. The samples were examined with a laser scanning confocal microscope, and images were analyzed and measured. The particles were categorized (or tabulated) into groups: 0-20, 21-50, 51-1000, and greater than 1000 μ. Chi-square analyses, with Bonferroni correction, were used to compare the proportion of particles among the undiluted and diluted drug formulations. RESULTS:: Dexamethasone and betamethasone sodium phosphate were pure liquid. The proportion of larger particles was significantly greater in the methylprednisolone and the compounded betamethasone preparations compared with the commercial betamethasone. There was no statistical difference between the commercial betamethasone and triamcinolone, although betamethasone had a smaller percentage of the larger particles. Increased dilution of the compounded betamethasone with lidocaine decreased the percentage of the larger particles, whereas increased dilution of methylprednisolone 80 mg/ml with saline increased the proportion of larger particles. CONCLUSION:: Commercial betamethasone is the recommended preparation if a nonsoluble steroid is preferred. Dexamethasone is a nonparticulate steroid, but its routine use awaits further studies on its safety and efficacy. [ABSTRACT FROM AUTHOR]