Temporal changes in cortical sensory processing during the transition from acute to chronic low back pain

Introduction: Sensory cortex activity differs between acute and chronic low back pain (LBP) with decreased activity in acute LBP but increased activity in chronic LBP. However, it is unknown how and when sensory cortex activity changes during the transition from acute to chronic LBP and whether fluctuations in sensory cortex activity are associated with pain sensitivity. Objectives: To examine (1) the trajectory of changes in sensory cortex activity over a period of six months from the onset of acute LBP; (2) the assoication between sesnory cortex activity and pain pain sensitivity. Methods: In a prospective cohort study (N 5 120), sensory evoked potentials (SEPs) were recorded using electroencephalography within 6 weeks of LBP onset (baseline) and at 3- and 6-month follow-up. Pain sensitivity was assessed using quantitative sensory testing (QST). Results: At baseline, individuals who developed chronic pain at 6-month follow-up exhibited less nonnoxious sensory processing (smaller area of N₈₀, N₁₅₀, and P₂₆₀ SEP components) compared with those who recovered. In individuals who recovered, SEP measures did not change over time. In individuals who developed chronic pain, N₈₀ and N₁₅₀ SEP area increased between baseline and 3 months, while P₂₆₀ SEP area increased between baseline and 6 months, reaching values consistent with those of recovered individuals. Sensory evoked potential measures showed no relationship with QST, except for a larger P₂₆₀ SEP area correlating with higher 6-month heat pain threshold at the site of LBP. Conclusions: Nonnoxious sensory processing in acute LBP was less in those who developed chronic pain than those who recovered. Nonnoxious sensory processing increased over time in those who developed chronic pain but was unchanged in those who recovered. In the transition from acute to chronic LBP, nonnoxious sensory processing in the sensory cortex was not associated with pain sensitivity.