Background/Purpose:

Chronic low back pain (LBP) is one of the most common musculoskeletal complaints in industrialized societies. It affects 80% of the adult population at some time in their lives and chronic LBP (CLBP) remained one of the most common causes of disability among adults in the past 20 years. One of the reasons for relatively low impact of current available treatment is the lack of a better pathophysiologic understanding of CLBP, reflected in the inconsistent response to the commonly used drug and non-drug treatments. Pain definition per se is at the very basis of the problem, due to its complexity and subjective experience encompassing the interpretation of nociceptive stimuli influenced by many factors. Some of the CLBP characteristics are reflected in brain processes probed by functional magnetic resonance imaging (fMRI).With that in mind we performed a study comparing neuronal correlates between CLBP with or without sick-leave

Methods:

Cross-sectional observational study comparing CLBP with or without sick leave with 74 volunteers divided into three groups: CLBP and sick leave [CLBP_L]; CLBP without sick leave [CLBP_NL]; controls  without pain]. fMRI was used during performance of two paradigms: pain and attention.

Results:

After acute painful stimulation (figure 1, 2 ),  higher  response at the anterior cingulate and superior frontal gyrus was observed in CLBP_NL vs. CLBP_L (p<0,001) and at the frontal pole and paracingulate region, comparing control vs. CLBP_L (p <0.001) showing a gradual modulation of thesel areas. We also observed a higher brain activity in the CLBP_NL compared to CLBP_L in superior frontal gyrus(p=0,047).

Conclusion:

Our results confirm and extend previous studies showing that chronic pain is associated with altered neuronal plasticity in brain areas that extend beyond somatosensory regions to include areas processing emotions. The lower activation of the superior frontal gyrus in the CLBP_L group in both tests (pain and attention) suggests a chronic preexisting activation in these areas. These results indicate that the modulation of acute pain and attention participates in the mechanism propagating chronic pain perception.

Figure 1 and 2

1

fMRI analysis in pain paradigm in CLBP_NL comparison > CLBP_L

(Anterior Cingulum and the superior frontal gyrus / medium right)

Values % BOLD Effect

2