Neural Structural Moderation of Sleep Architecture-Pain Relationships in Fibromyalgia and Insomnia: A Pilot Study

Chronic pain and insomnia are independently associated with neural structural alterations compared to healthy controls. However, the relationship between their joint association and cortical thickness (CT) in pain processing regions is unknown. This preliminary study explores whether CT in regions of interest (anterior cingulate cortex-ACC; insula) moderates associations between sleep architecture and overnight pain changes.

Thirty adults with fibromyalgia and insomnia (M_age = 57.2, SD = 13.1) completed 1-night of polysomnography, 14 daily diaries documenting evening/morning pain (0:none-100:worst imaginable), and magnetic resonance imaging (MRI). Overnight pain changes were computed as average differences between evening/next morning pain (positive values = lower morning pain, negative values = worse morning pain). CT values (Left/Right rostral/caudal ACC, Left/Right insula) were extracted from MRI data using FreeSurfer 5.1.0. Multiple regressions examined whether CT moderated associations between sleep architecture (N1-N3%, REM%) and overnight pain changes, controlling for age and education.

Right rostral ACC (RrACC) CT moderated associations between overnight pain changes and N2%, N3% and REM%. At highest RrACC CT, lower N2% was associated with lower morning vs. previous evening pain; and greater N3% and REM% were associated with lower morning vs. evening pain. Left insula CT moderated associations between N3% and overnight pain changes. Greater N3% was associated with lower morning pain relative to evening pain at highest Left insula CT.

Greater CT inpain processing regions (RrACC, left insula) moderates associations between greater restorative sleep and overnight pain improvements. Further examination of cortical thickness in research seeking to understand the sleep/pain relationship in fibromyalgia is warranted.