Pain Inhibition and Facilitation in Recurrent Low Back Pain

Pain inhibitory and facilitatory mechanisms have been suggested to play a role in the development of persistent low back pain; however, there is still debate on when changes in these mechanisms occur. Similarly, evoked cortical responses can reflect neuroplastic changes in pain processing regions, which are also thought to play a role in the transition to persistent pain, but there is also debate on when these neuroplastic changes develop relative to low back pain. Therefore, this study will use patients with an intermediary clinical pain state, recurrent low back pain, and matched healthy control participants, to investigate within and between subject differences in pain inhibitory, facilitatory and neuroplastic mechanisms.

Primary outcomes

• Conditioned Pain Modulation [Day 0 vs. Day 28]: Pressure pain threshold (kPa) as test stimulus before compared to during a pressure conditioning stimulus on the lower leg
• Temporal Summation of Pain [Day 0 vs. Day 28]: Pain rating (VAS) change over a series of 10 repeated mechanical stimuli

Secondary outcomes

• Pressure Pain Thresholds [Day 0 vs. Day 28]: Threshold of pain detection (kPa) with handheld algometry over the low back and distant sites
• Thermal Pain Thresholds [Day 0 vs. Day 28]: Hot and cold pain detection thresholds (degrees)
• Two Point Discrimination [Day 0 vs. Day 28]: The smallest distance (mm) for which two separate points can be distinguished over the low back
• Proprioceptive Weighting [Day 0 vs. Day 28]: Center of pressure displacement during 1-minute of quiet standing
• Sensory Evoked Potentials [Day 0 vs. Day 28]: EEG signals recorded in response to laser and electrical stimuli applied to the back

Other outcomes

• Affective Regulation [Day 0 vs. Day 28]: Pressure pain ratings pre, during and post affective image set
• Attentional Regulation [Day 0 vs. Day 28]: Pressure pain ratings pre, during and post computerised attention-demanding task

Sex: All, ages: 18 Years to 60 Years, accepts healthy volunteers

Inclusion:

* Healthy men and women
* Aged 18-60 years
* No previous back pain OR >1 previous episode of low back pain in past 12 months
* No current back pain OR Pain in the region posteriorly between the inferior border of the 12th rib and the lower gluteal fold (low back pain) at time of recruitment lasting >24 hours
* Able to speak, read and understand English

Exclusion:

* Pregnancy
* First episode of low back pain
* Low back pain associated with menstruation
* Chronic low back pain (continuous pain episode for >3 months)
* Currently seeking active treatment for low back pain
* Red flags symptoms
* Drug addiction defined as the use of cannabis, opioids or other drugs
* Current or previous neurologic, musculoskeletal, mental, or other illnesses which may affect the trial
* Current or previous chronic or recurrent pain condition other than low back pain
* Current regular use of analgesic or other medication which may affect the trial
* Lack of ability to cooperate
* Recent history of acute pain particularly in the lower limbs (unless related to LBP)
* Abnormally disrupted sleep in 24 hours preceding experiment

• Results publication: McPhee ME, Graven-Nielsen T. Positive affect and distraction enhance whereas negative affect impairs pain modulation in patients with recurrent low back pain and matched controls. Pain. 2022 May 1;163(5):887-896. doi: 10.1097/j.pain.0000000000002442. PMID 34382603

• Megan E McPhee, BPhty MSc, Principal investigator, Aalborg University