Epidural interferon gamma-immunoreactivity: a biomarker for lumbar nerve root irritation.

Study Design: Prospective observational cohort.

Objective: Correlate epidural inflammatory cytokines with the clinical response to epidural steroid injection in patients with lumbar nerve root irritation.

Summary Of Background Data: Some back pain syndromes are thought to be associated with activation of inflammatory pathways and others may be associated with primary mechanical derangements. Human studies providing detailed evidence for the primary inflammatory causation, which may be best treated with anti-inflammatory strategies, are lacking. There are currently no accurate diagnostic tests to predict the response to epidural steroid injection or surgical intervention in back pain and sciatica syndromes. METHODS.: Forty-seven consecutive patients with lumbar degenerative changes and low back and/or leg pain were prospectively enrolled. An epidural lavage was performed, followed by injection of marcaine/depo-medrol. Subjects scored their pain before and 3 months after the procedure. The immunoreactivity of an array of cytokines was measured in lavage samples and compared with clinical response to the therapeutic injection. Ten subjects underwent repeat epidural lavage sampling 3 months after the steroid injection.

Results: Interferon gamma (IFNgamma) was the most consistently detected cytokine. IFNgamma-immunoreactivity also highly correlated with reported reduction of pain 3-months after the epidural steroid injection. In subjects reporting significant pain relief (>50%) from the injection, mean [IFNgamma] was significantly greater compared with patients experiencing no significant relief. The IFNgamma-immunoreactivity in repeat lavage samples decreased to trace residual concentrations in patients who reported pain relief from the steroid injection.

Conclusion: The presence of epidural IFNgamma-immunoreactivity corresponding to >10 pg/mL predicted significant pain relief after epidural steroid injection with >95% accuracy. These results suggest that IFNgamma may be part of a biochemical cascade triggering pain in sciatica; IFNgamma-immunoreactivity may aid as a biomarker for predicting the response to steroid therapy and/or surgical intervention, and may serve as a future therapeutic target.