Published: Sep 16, 2013 | Updated: Sep 16, 2013

By Nancy Walsh, Staff Writer, MedPage Today

Full Story:  http://www.medpagetoday.com/PainManagement/Fibromyalgia/41626

Action Points

• Individuals seeking care for back pain whose symptom pattern was typical of fibromyalgia derived little benefit from minimally invasive spine therapies such as epidural steroid injections.
• Note that on univariate analysis, patients who met the criteria for fibromyalgia had higher scores for pain severity and interference, neuropathic pain, anxiety and depression, and worse physical function, all differences compared with nonfibromyalgia patients.

Individuals seeking care for back pain whose symptom pattern was typical of fibromyalgia derived little benefit from minimally invasive spine therapies such as epidural steroid injections, researchers found.

Among patients presenting to a back pain treatment center, 42% met the American College of Rheumatology (ACR) survey criteria for fibromyalgia, according toChad M. Brummett, MD, and colleagues from the University of Michigan in Ann Arbor.

In a final model based on multivariate analyses, factors that were independently associated with a diagnosis of fibromyalgia were female sex, neuropathic pain, physical function, anxiety, and pain interference (P<0.01 for all variables), they reported.

“The independent predictors from the multivariate models are some of the most commonly described predictors of poor outcomes in minimally invasive spine interventions and post-surgical pain. Hence, there may be a common underlying pathophysiology or ‘diagnosis’ driving these findings,” the researchers wrote online in Arthritis & Rheumatism.

In recent decades the popularity of minimally invasive spine treatments has skyrocketed, with increases of more than 100% being reported for epidural steroid injections and of more than 500% for facet joint interventions such as injections and medial branch blocks.

However, these procedures have high failure rates, with estimates ranging from 25% to 45%, and a recent meta-analysis found little long-term benefit for spine injections for sciatica.

Previous research has suggested that poor response is associated with young age, use of opioids, previous spine surgery, and lengthy duration of symptoms, as well as somatization and depression.

It also has become clear that certain chronic pain conditions, most notably fibromyalgia, are characterized by alterations in centralized CNS pain processing, implying that local treatments are less likely to be successful.

“Injections and peripherally targeted analgesics would be expected to provide less benefit in a patient with altered central pain processing than in those with predominantly peripheral pathology,” the researchers noted.

Patients with fibromyalgia also typically have reduced levels of pain-inhibiting neurotransmitters such as serotonin and high levels of transmitters such as glutamate that can increase pain sensations.

To explore whether this centralized pain phenotype was common among spine patients and might help aid in patient selection for localized treatments, Brummett’s group enrolled 443 patients with complaints ranging from neck pain to lumbago and lumbar spinal stenosis.

Fibromyalgia was diagnosed according to the ACR 2010 criteria, which was based on a widespread pain index and a symptom severity scale and no longer included the original tender point criteria.

A continuous fibromyalgia score consisted of the sum of the pain index and severity scale score.

Other diagnostic evaluations included the Brief Pain Inventory, which measures pain severity and interference, PainDETECT for neuropathic pain, the Hospital Anxiety and Depression Scale, and physical function according to the Oswestry Disability Index.

On univariate analysis, patients who met the criteria for fibromyalgia were more often younger (47 versus 52 years, P=0.001), not employed (25% versus 41%, P=0.005), and to have financial compensation (33% versus 18%, P=0.0005).

They also had higher scores for pain severity and interference, neuropathic pain, anxiety and depression, and worse physical function (P<0.0001 for all), which represented “profound phenotypic differences” compared with nonfibromyalgia patients, the researchers observed.

On a multivariate linear regression analysis, looking at an association between the continuous fibromyalgia score, pain variables, and phenotype, significant associations were seen for female sex (P=0.0002), pain interference (P=0.0047), neuropathic pain (P<0.0001) and anxiety (P<0.0001).

And on a logistic regression analysis that considered fibromyalgia as a binary variable, significant associations existed for neuropathic pain (P=0.0002), physical function (P=0.024) and anxiety (P<0.0001).

The final model had a high area under the curve receiver operating characteristic (C statistic) for fibromyalgia of 0.80.

“Taken together, these data make a compelling case for the study of a modified treatment approach. For example, previous studies have demonstrated efficacy for serotonin-norepinephrine reuptake inhibitors in chronic low back pain,” the researchers wrote.

“Nonpharmacologic interventions, such as cognitive-behavioral therapy and exercise have also demonstrated excellent effect sizes that often exceed pharmacologic interventions in fibromyalgia and other pain states,” they added.

Limitations of the study include its single site and cross-sectional design, and further objective research will be needed such as neuroimaging to corroborate these findings.

Nonetheless, the researchers concluded, “It is possible that a simple self-report measure could aid in the prediction of outcomes in some of the most common minimally invasive spine interventions.”