Time-dependent effect of epidural steroid on pain behavior induced by chronic compression of dorsal root ganglion in rats.

Although epidural steroid injection has been commonly used to treat radicular pain, its clinical efficacy remains controversial. In a rat model of radicular pain induced by chronic compression of lumbar dorsal root ganglion (CCD), we examined the effect of epidural steroid on CCD-induced pain behavior. Triamcinolone [a glucocorticoid receptor (GR) agonist] or RU38486 (a GR antagonist) was given epidurally once either on day 3 (early treatment) or day 10 (late treatment) after CCD. The results showed that 1) early treatment with triamcinolone and RU38486 alone, respectively, reduced and exacerbated mechanical allodynia and thermal hyperalgesia, 2) late treatment with triamcinolone alone failed to improve mechanical allodynia and only transiently attenuated thermal hyperalgesia, and 3) late treatment with RU38486 alone improved mechanical allodynia and thermal hyperalgesia in CCD rats. Moreover, a second dose of triamcinolone given on day 10 paradoxically exacerbated pain behavior in CCD rats that received a first dose of triamcinolone on day 3. These results indicate that the effect of epidural steroid on radicular pain may be time-dependent. Clinical implications for epidural steroid treatment are discussed in light of these preclinical findings.