Steroids effect two processes/receptors – a glucocorticoid pathway, and a mineralcorticoid one. The glucocorticoid pathway has strong anti-inflammatory and immunosuppressive effects. The mineralcorticoid pathway works more on retaining salt. The latter has been found to have pro-inflammatory effects which might have a pain increasing effect, blunting benefits of steroid injections. This might explain the lackluster effects and duration of epidural injections.
Mol Pain. 2013 Mar 28;9:17.
Preclinical studies of low back pain.
Strong JA, Xie W, Bataille FJ, Zhang JM. free article here
- Glucocorticoid effect on nerve root damage might be variable:
“In two rat studies using a CCD model, the clinically used glucocorticoid triamcinolone applied epidurally reduced pain behaviors when given 3 days after the compression
began [10,49]. However, different results were obtained when applying drugs at day 10; at this later time point, triamcinolone failed to improve pain behaviors while
a glucocorticoid antagonist improved them Additional preclinical research is needed to address other possible reasons for limited efficacy of steroids, such as central sensitization or presence of an ongoing inflammatory stimulus in some forms of low back pain.” - Mineralcorticoids “may promote type I inflammation”
- Animal nerve pain is minimized by blocking mineralcorticoid receptors
Comment – Looks like to obtain good results from steroids one has to include something that blocks minerocorticoids and/or the cytokines they stimulate. Entanercept (Enbrel) blocks one of those cytokines (Tumor Necrosis Factor = TNF) but it has been suggested that the mixed results with that agent are due to fact TNF is more important early on in sciatica.
There are other reasons why steroid epidurals do not work well
- the injection could end up on the wrong side of the epidural septum:
Epidural Primarily Work on Side Needle Tip is Closer To - Lying patient down for 20+ minutes with bad sound down will almost double effectiveness:
Steroid Epidurals – Why Some Work And Some Not So Well - It also looks that waiting 6 weeks after acute sciatica to decide if you should give an epidural might not be wise idea – and early on, entanercept could be used; but not at the low dose of 4 mg that failed miserably in a recent trial epidurally:
Cohen SP, White RL, Kurihara C, Larkin TM, Chang A, Griffith SR, Gilligan C, Larkin R, Morlando B, Pasquina PF, Yaksh TL, Nguyen C
Epidural steroids, etanercept, or saline in subacute sciatica: a multicenter, randomized trial.
Ann Intern Med 2012, 156(8) April :551–559 abstract here
25 mg TWICE, separated by a week, paraspinously was used in original studies