Patients with chronic sciatica have evidence of inflammation in key areas of the nervous system, researchers have found.
Sciatica causes pain that radiates out from the lower back, down the buttocks and into one or both of the legs. It usually gets better in four to six weeks but can last longer.
A study published in the May issue of the journal Pain revealed that average levels of a marker of neuroinflammation were elevated in both the spinal cord and the nerve roots of patients with chronic sciatica.
The research team at Massachusetts General Hospital (MGH) also found that levels of neuroinflammation differed between those whose pain was relieved by anti-inflammatory steroid injections and those for whom the treatment provided little relief.
In the study, 16 patients with chronic radiculopathy and 10 control volunteers had combined MR and PET imaging with a radiopharmaceutical that binds to TSPO, a marker for neuroinflammation. The scans focused on neuroforamina in the lumbar spine for all participants, and in a subset of 18 -- nine patients and nine controls -- images were also taken of the sections of the lower spinal cord that are connected to the nerve roots affected in sciatica.
Compared with those of control participants, TSPO levels in sciatica patients were higher in both the neuroforamina and the spinal cord. The sciatica-associated elevations were seen in nerve roots on the side of affected legs and in spinal cord segments known to process sensory signals from the legs. Among nine patient participants who received steroid injections as part of their clinical care -- two before the scans and seven after -- only five experienced significant relief from the procedure, and those five all had results indicating higher neuroforaminal TSPO levels, MGH reported.
"The fact that patients with stronger TSPO elevations in the nerve roots benefited most from a local anti-inflammatory treatment makes sense," said co-senior author Marco Loggia, of the Martinos Center for Biomedical Imaging at MGH. "For patients who didn't benefit from steroid injections, the source of pain and inflammation may be the spinal cord or, as shown in our previous paper, the brain itself."
"If larger studies confirm that the efficacy of steroid injections correlates with nerve root inflammation, physicians will have a way to identify which patients are most likely to benefit from the procedure," added co-senior author Yi Zhang, of the Center for Pain Management in the MGH Department of Anesthesia, Critical Care and Pain Management. "Our results also suggest that directly treating neuroinflammation in the spinal cord may help patients who don't respond to steroid injections."